# Why THAC0 Rocks



## Thondor (Mar 1, 2009)

There has always been a rhetoric on these boards that discredits THAC0 (To Hit Armour Class 0) as being by far inferior to BAB (Base Attack Bonus). Posters state this as a matter of course, saying things like the adjustement to BAB (from THAC0) was so inherently logical that it is stunning that it didn't happen earlier.

I will attempt to explain here why THAC0 was created, how it works and why it is in fact simpler, speeds up play, and better then BAB.

Able to write a history of the evolution of THAC0 I am not. I know that in the 1e DMG both combat tables and THAC0 were used. And that BAB began in 3rd edition.

1. _With THAC0 you know wether you hit on a tie or not._ (This is the same with the saving throw tables in 1e/2e etc by the way.) There is no inherent logic that tells you wether you hit on a tie with BAB, wether you make a save on a tie, wether you beat the DC of a skill cheque on a tie.  (Yes it says this on p.62, p.134, in the 3.5 PHB. However these are in isolated places and are not inherent to the definition. As far as I can tell, it does not actually say wether or not saving thows  win on a tie.) With THAC0 the name itself says it all. If you have a THAC0 of 17, you must roll a 17 to hit a Armor Class of 0.

2. _Ease of Use. _A character who had a BAB of +5 would have a THAC0 of 15. Compare
A 3e character with a BAB of +5 tries to hit a enemy with a AC 15. Player rolls a 7, (ummm 7 plus 5 is 12) hey DM I got a 12.  DM you miss. Next round, Player rolls a 13, (umm 13 plus 5 is uh 18), hey DM I got a 18. You hit. Next round, player rolls a 8 (umm, 8 plus 5 is 13), hey DM I got a 13. DM you miss.
A  pre-3e character with a THAC0 of 15 tries to hit an enemy with a AC 5.
Player rolls a 7. Player says "7", DM says "you miss". (The DM knows that no one around the table has a THAC0 better then 14.) Next round, Player rolls a 13, says 13 DM says you hit (DM knows that everybody around the table but the wizard has a THAC0 of at least 18.) Next round, player rolls a 8, "I rolled an 8", DM is distracted "What's your THAC0?" Player "15", Dm thinks (15 -5 = 10) "You miss."

Let me explain that a little better in a different way and we'll get to another one of my points:
3. _THAC0 means you do *one* calculation per different AC of opponent._
Same example THAC0 15 character trying to hit AC 15. This DM doesn't mind letting the players know the opponents AC.

Another player has attacked the same creature already. The DM informed them the AC was 5. _Before rolling_ the player thinks to himself 'My THAC0 is 15 - 5 AC= 10, I need to roll a 10 or better to hit, sweet 50% chance!' (actually its a 55% chance) Informed that he's next, the player rolls a 7 "7! darn I miss." DM "OK next person". Next round, Player rolls a 13, "Yes a 13, I hit". Next round, Player rolls a 8, "8! I think I miss, 15-5 yeah I miss."

compared to:
DM says alright the AC is 15. the player has a BAB of +5.   
First round: Player rolls a 7. 7+5 =12. "I got a 12, I miss."
Second round: Player rolls a 13. 13+5 =18. "I got a 18, I hit."
Third round: Player rolls a 8. 8+5 =13. "I got a 13, I misss."

With THAC0 you figure out what number you need to roll on the die once. With BAB you roll the dice, add your modifier, and compare it to the target number . . . every single attack.


I have found that THAC0 leads to much, much, quicker combat. For some reason people have an inherent fear of substaction, and have difficulty overcoming the initial conceptualization of THAC0. Which is really quite simple. 

THAC0 - opponents AC = number you need to roll on the dice.

the 'complicated example' that many state of a negative AC is really simple: Say an AC -2, THAC0 15. 
15 - - 2= 15 +2= 17. not difficult.


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## Chaos Disciple (Mar 1, 2009)

Thondor said:


> THAC0 - opponents AC = number you need to roll on the dice.





The advantage with the 3e version is that both the Target Number and BAB gain bonuses (this removes the confusion over the lower AC #= better AC)


But basiclly its the same formula, only reversed

Target number(Def) - BAB(Att) = number you need to roll on the dice.


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## Agamon (Mar 1, 2009)

Personally, having played both ways for a number of years, I disagree, for two reasons:

1. Adding is inherently easier than subtracting.

2. Spreading the math from the one DM, who already does way more mental work than the players during the game, to the many players, is easier over the game night.


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## S'mon (Mar 1, 2009)

"With THAC0 you figure out what number you need to roll on the die once. With BAB you roll the dice, add your modifier, and compare it to the target number . . . every single attack."

I agree - this does make THAC0 easier to use, where AC is known.  You can do the same with ascending AC by deducting your attack bonus from the AC to get target number, but it's less intuitive.


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## BryonD (Mar 1, 2009)

Thondor said:


> compared to:
> DM says alright the AC is 15. the player has a BAB of +5.
> First round: Player rolls a 7. 7+5 =12. "I got a 12, I miss."
> Second round: Player rolls a 13. 13+5 =18. "I got a 18, I miss."
> Third round: Player rolls a 8. 8+5 =13. "I got a 13, I misss."



lol

So your evidence requires that the player roll a 13 one round and find out it is a miss and when he rolls an 8 the next round, for some reason he needs to "do the math" to find out if the 8 is better than the 13 or not.  

Sorry, but the fundamental math is the same, just with BAB it is vastly more intuitive.

THAC0 isn't hard.  But I could just as easily reverse your example and have the THAC0 player repeating his math every time while the BAB guy just remembers what he needed.  It works the same.  The only difference is whether or not one applies a bogus misleading example where the player does it correctly for one system and really stupidly for the other.  

The math is the same.  I have seen people get which number you subtract mixed up with THAC0.  Not often, but it is easy to do by mistake.

BAB is easier because A+B = B+A.
THAC0 is less intuitive because A - B <> B - A


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## Lanefan (Mar 2, 2009)

I've been running 1e for 25-odd years and still haven't figured out THAC0.  To me, it just adds an unnecessary layer of complication - I don't care whether a swing hits AC 0, I care whether it hits the specific AC of the particular opponent at the time - all I want to know is whether the base roll, bonuses, penalties, fight level, and AC end up adding to 21 or more.  THAC0 doesn't help me there, and instances of both the target's AC being 0 and the attacker's listed THAC0 rating being accurate for the situation happen rarely enough that I'm not going to waste the time checking.

Lanefan


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## Thondor (Mar 2, 2009)

BryonD said:


> lol
> 
> So your evidence requires that the player roll a 13 one round and find out it is a miss and when he rolls an 8 the next round, for some reason he needs to "do the math" to find out if the 8 is better than the 13 or not.
> 
> ...




Well that's my fault for copy an pasting and not editing. The middle one hits of course. So there is a reason for him to "do the math again". In my experience most players seem to do the math again with BAB anyway.
Seeing as you quoted me to reserve my error for posterity, I will go back and edit my first post in order that future readers arn't confused by my error.

In your example what's A and what's B? I'll be plain with you and admit I don't know what your getting at.

To me THAC0 is easier because the _math_ is a constant, i.e. for one opponent and one attacker it is always the same.
eg: x (The only variable in either equation) is the number rolled on the dice.

Using THAC0: if x => THAC0 - AC it hits
Using BAB: if x + BAB => AC 

So if a player wants to figuer out what they need to roll with BAB, they can. But they need to rearrange the equation in their head. 
( x+BAB => AC
x + BAB - BAB => AC - BAB
x=> AC - BAB)
Which certainly isn't 'intuitive' and is actually exactly what THAC0 is. (S'mon basically said this above, far more eloquently then I have.)

The trick with THAC0 is figuring it out _before_ the roll is made.


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## Umbran (Mar 2, 2009)

It takes more verbiage to explain why THACO is simpler and easier than it takes to explain BAB to begin with.  That says to me that THACO is not, in fact, actually simpler and easier.

YMMV, of course.


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## Thondor (Mar 2, 2009)

Lanefan said:


> I've been running 1e for 25-odd years and still haven't figured out THAC0. To me, it just adds an unnecessary layer of complication - I don't care whether a swing hits AC 0, I care whether it hits the specific AC of the particular opponent at the time - all I want to know is whether the base roll, bonuses, penalties, fight level, and AC end up adding to 21 or more. THAC0 doesn't help me there, and instances of both the target's AC being 0 and the attacker's listed THAC0 rating being accurate for the situation happen rarely enough that I'm not going to waste the time checking.
> 
> Lanefan




That's . . . unfortunate. You can always use those handy combat tables to speed things up!

Once again I'll have to admit that I don't understand what your getting at with your example, why would you want it all to add up to 21 or more? Ah I think I get you. AC 0 = AC 21 .  . .  which still leaves me confused. It's wonderful if the monsters AC is 0/21, because then THAC0 tells you _everything you need to know -- _you don't need to do any math. Just roll your THAC0 rating or better. In all other cases THAC0(including modifiers) - the AC (including modifiers) = what you need to roll to hit. untill that opponent is dead or you pick a new one -- which probably has the same AC.  

Of course bonuses and penalties are rarer in AD&D then in 3e, especially modifiers that won't always effect your combat ability (eg spells, distance for ranged weapons). Still as long as you realize that _every* _number in 1e improves by going down, you should do fine. The lower the AC, THAC0 or Save the better.  (even surprise is better the lower it is. surprised on a 1 on a d6, is better then surprised on a 3)
People seem to find this confusing because rolling higher is almost always better. 

* a slight exageration. I believe Spell Resistance is better the higher the % is. I can't think of any other subsystem (psionics? maybe) that does though.


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## Korgoth (Mar 2, 2009)

Agamon said:


> 1. Adding is inherently easier than subtracting.




Is it? I feel pretty confident with both operations.


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## El Mahdi (Mar 2, 2009)

Six of one, half-dozen of the other.

It seems as if they're both just different paths to the same destination. 

Different people like different views or modes of transportion, but they all end up at the same place.  (However, personally I prefer BAB.  To me, the BAB path seems to be a little less rocky.)


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## GMforPowergamers (Mar 2, 2009)

10 years out of date here...but lets see how I do...


   Ok I am a 3rd level fighter...I have a thac0 of 18...I have a +1/+3 str and weapon specilization +1/+2, and a +2 long sword....


       I roll a 12 I add 4 (2 magic 1 str 1 training) and have a 16...I subtract my 18 thac0 and have 2...so I hit AC 2 then I would roll 1d8+7 for damage

     we use to have adjusted thac0...so above I would write on the sheet
 in the Thac0 box     18/14


      Now adays I would have +X....lets say 3rd level fighter 16 str and weapon focus longsword...and a MW longsword   
      +8   1d8+3

     Now I roll a 12 in eaither case I know I hit AC 20 or AC 2...the math is simple in play...but hard to explain, and not that simple to learn the old way...


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## Thondor (Mar 2, 2009)

Umbran said:


> It takes more verbiage to explain why THACO is simpler and easier than it takes to explain BAB to begin with. That says to me that THACO is not, in fact, actually simpler and easier.
> 
> YMMV, of course.




Here's me explaining THAC0: the number you roll >= THAC0 - AC

Here's me explaining BAB: the number you roll + BAB => AC

it is in fact the exact same amount of words. Explaining why one is _better_ then the other will of course take substantially more verbiage. _No matter what side you take._

Which says to me that unfortunately your point is illogical. I do however value your imput, and would welcome further criticism.


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## BryonD (Mar 2, 2009)

Thondor said:


> In your example what's A and what's B? I'll be plain with you and admit I don't know what your getting at.



Look at your own example.
THAC0 requires subtraction which requires keeping the numbers straight.
BAB is addition, the elementary level commutative property applies.

In your "easy" example you have jumped to the (rather poor) presumption that the AC is always known.  Yet in the BAB example the DC is unknown and must be checked against each time.  You are still requiring the BAB player to be intentionally dumb while giving the THAC0 example player a the presumption of knowledge and correct procedure.

You are basing the arguement 100% on this stacked deck presumption.

Again, THAC0 is easy.  I'm not arguing with you there.  But BAB is is every bit as easy AND it is more intuitive to 90%+ of people.



> To me THAC0 is easier because the _math_ is a constant, i.e. for one opponent and one attacker it is always the same.
> eg: x (The only variable in either equation) is the number rolled on the dice.
> 
> Using THAC0: if x => THAC0 - AC it hits
> ...



You are talking about addition and subtraction with numbers in the 1 to 30 range.
It ain't rocket science.

If you don't know AC then BAB is easier because you can tell the DM your total and he knows if you hit or not.  If you don't know AC with THAC0 then you have to tell the DM your THAC0 and the roll.  And you must keep the numbers straight.

If you do know the AC, then it is 2nd grade math to get the target roll number under either system.  Perhaps THAC0 is easier for C- level 2nd graders.  I'm not so sure though.

But if the getting a target number out of BAB is difficult for someone, then I probably just can not relate to their perception of the system.

But to virtually every gamer I've ever played with, BAB is THAC0 presented in the way that humans actually think.


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## Thondor (Mar 2, 2009)

GMforPowergamers said:


> 10 years out of date here...but lets see how I do...
> 
> 
> Ok I am a 3rd level fighter...I have a thac0 of 18...I have a +1/+3 str and weapon specilization +1/+2, and a +2 long sword....
> ...





Well actually the way you did it is harder and is confusing, and actually wrong.
You Took the roll, add modifiers, then substracted THAC0 which actually results in a negative 2 not positive 2. and then you compared it to AC.

You don't compare your roll to AC. You compare your roll to THAC0 - AC. if your roll was that number or better you hit.

First of course you would already have include all the modifiers in your "long sword THAC0" just like you figure out for your "long sword Attack bonus"  (Your right it is 14, just like its +8)

So you roll a 12, does that hit? 14-2 =12 so yes it does.


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## Thondor (Mar 2, 2009)

BryonD said:


> Look at your own example.
> THAC0 requires subtraction which requires keeping the numbers straight.
> BAB is addition, the elementary level commutative property applies.
> 
> ...




Actually I was extremely careful that in the example in number 2, neither player knows the AC. And in number 3, they both know the AC.

I did give the DM in the example number 2 (where AC was hidden) a small advantage over the player doing the addition. But that is because well the DM usually has some manner of advantage.

With THAC0 the DM decides if s/he wants to do the math (by hiding the AC) or wants the players to (By giving the AC). In all cases with BAB the Player does the math. Another advantage in my opinion.


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## Thondor (Mar 2, 2009)

I do admit that understanding how THAC0 functions is slightly more difficult conceptually. However, it more then makes up for it in accelerating game play. It is a concept that is easily explained by doing it though. 

Player: I don't get this THAC0 thing, why does AC go down?
DM: Both AC and THAC0 go down, lower is better. Your character has a THAC0 of 20 right
Player: Yeah
DM: Suppose you want to beat up and average bloke. He's not wearing any armour or particulary good at dodging, so his AC is 10.
Player: Um . . . OK . . .
DM: To know what you need to roll on this dice (holds up a d 20) in order to hit him, all you do is minus the AC from your THAC0
Player: oh, so 20 - 10, 10.
DM: Roll the dice
Player: It's a 12, so I guess I . .. hit.
DM: you hit, now you roll damage. Sometimes I won't tell you the AC, so you just tell me what you roll and I'll figure out if you hit.

Yeah it can be a little DM heavy. If you want it to be. Still remebering a few players THAC0 isn't that tough. And you can just ask. Most of the time it'll be obvious though. Hmm he rolled really high. hit. really low miss. You _can_ do this with BAB to of course but it's harder.

One of the things that troubles me with BAB as a DM is that my players often say what they rolled and what they actually got (roll+BAB) which leads to confusion. Player " 17" DM "you missed", Player "what!? Last time I roll a 14 and hit!" DM "sigh, did you roll a 17 or get a 17?"
(note these players never played with THAC0 and should no better )


_an aside_
The mere fact that a DM can tell a player what they need to roll to hit, means it is much easier for those who have some difficulty with math ( in some cases because their Kids) to play.


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## Freakohollik (Mar 2, 2009)

The only point in your argument that I find to be partly valid is when using THAC0, it is implied that players know the opponenets' ACs. You can get the same speed up from BaB if the DM decides to tell the players the AC values, and the players then figure out what they need to roll before they roll. The difference is that the THAC0 system almost required you to know the opponent AC, where as BaB system implied that the players should not know the opponents' AC.


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## Remathilis (Mar 2, 2009)

Thondor said:


> Well actually the way you did it is harder and is confusing, and actually wrong.
> You Took the roll, add modifiers, then subtracted THAC0 which actually results in a negative 2 not positive 2. and then you compared it to AC.
> 
> You don't compare your roll to AC. You compare your roll to THAC0 - AC. if your roll was that number or better you hit.
> ...




See that again assumes your DM has told you the target AC. As a DM, I rarely ever tell the AC of a foe (in any edition).

So if I roll my longsword attack (thac0 14) I know two parts of the equation, my roll and my thac0. I don't know my foe's AC. So my only option is Thac0 - roll = AC, not Thac0 - AC = roll.


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## Ariosto (Mar 2, 2009)

Some prefer one expression, some the other, of what is fundamentally the same thing. Still others prefer starting with a table look-up to needing always to engage in arithmetic -- and 1st edition AD&Ders may appreciate the subtlety of repeating 20s.

In my experience, what actually seems to appeal most to players (if they want to be concerned with the mechanic at all, rather than leaving it to the DM) is a table on the character sheet. Class, level, proficiency, strength, magic, the peculiarities of a guisarme-voulge ... all can be figured in already. Just look up the relevant Armor Class, and beneath it is the number needed.


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## I'm A Banana (Mar 2, 2009)

I hear Time Cube is easy to explain, too. 

THAC0 is counter-intuitive. I roll a dice, and I know if I hit AC0, but unless the monster has an AC of 0, I still have to do math to find out of this particular monster is hit.

AC vs. BAB is more intuitive. I roll a dice, and I know if I beat a number. All the math I do applies to the die roll itself, rather than to an abstract number on a chart. 

It's more of a psychological thing than a rational thing, but games are all about psychology, so....

Of course, you might like THAC0 and think it rocks. BAB, I think, tends to work better for more people than THAC0 does. But don't let my opinion stop you from rocking out however you want...D&D's lovely for that most of the time.


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## Mercutio01 (Mar 2, 2009)

I never understood THAC0 as a mathematical function.  In fact, until I saw it plainly written here, I don't think I would ever have been able to explain it.  I used to just use a little line table on my character sheet with the ACs ranging from -X to +X.  Underneath I would write the THAC0s, as below.

-2 -1  0  +1 +2 +3 +4 +5
22 21 20 19 18 17 16 15

When I'd roll, I would just look at my mini chart and tell the DM what AC I hit.

For me, rolling a d20 and adding my bonus and then telling the DM what I hit was infinitely easier.  It was by far THE systemic alteration that made me switch from 2E to 3E


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## Ariosto (Mar 2, 2009)

"Six of one, half a dozen of another." The _Monster and Treasure Assortments_ included "THAC9," as I recall.

Now, one nifty trick with a "roll-under" approach is to avoid subtraction by calling for a roll _over_ a penalty.


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## kenmarable (Mar 2, 2009)

I have no problem with people who prefer THAC0, but for me personally, that was one aspect I was very happy to see replaced. Re-done saves for 3.0 were also great. Sure, with both THAC0 and BAB, the math is easy for a elementary school kid, but overall, there were some really unnecessary complexities.

Having new players not have to draw little up or down arrows next to all their numbers in order to remember which ones were "high number = good" and which were "high number = bad" is bonus in my book. ("I have a strength of 18/70%, save vs. Rod, Staff, Wands of 6, 65% pick locks, and AC of -2.") I played so long, it was all intuitive. But I introduced a lot of players to the game during 2e, and the most common question was always whether a high or low number was good. There was no real design consistency at all across the board.

Plus, having pretty much everything in the game (attacks, saves, skill checks, ability checks) all being "roll d20 and add you modifier, try to hit a target number" makes the game SO much better for me and the people I game with. As much as I loved all those years of OD&D, 1e, and 2e (and yes, I did really enjoy 2e), I have ZERO interest in ever playing those systems again. Nothing wrong with others who do enjoy it - they aren't bad systems. But for me personally, THAC0 is fun to look back on, but not something I ever want to think about during a game again.


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## Chaos Disciple (Mar 2, 2009)

Sorry if this is a little off topic




S'mon said:


> "With THAC0 you figure out what number you need to roll on the die once. With BAB you roll the dice, add your modifier, and compare it to the *target number* . . . every single attack."
> 
> I agree - this does make THAC0 easier to use, where AC is known. You can do the same with ascending AC by deducting your attack bonus from the AC to get *target number*, but it's less intuitive.





S'mon

You used the term "target number" in two differnt ways. 
First as the AC (or Defense #).
Second as the number rolled on the dice.


I believe the first one was correct. But personally I would prefer the term "target number" to refer to the number you have to roll.

Anyway
Just an observation-carry on


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## Hussar (Mar 2, 2009)

There's one problem of THAC0 that hasn't been addressed.

AC in 3e or 4e is not limited to -10.  You have AC's in the (if you translated) -20 or -30 range at higher levels.  THAC0 suddenly becomes a lot trickier when you have +47 to hit.

Player:  Hey, I have a THAC0 of -27, I roll a 14, I guess I hit an AC of minus 51.  Do I hit?

The numbers in 3e and 4e are such that limiting yourself to a range of AC's from 10- -10 just doesn't work, and once you get beyond those AC's, THAC0 become much more difficult to use.


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## Philotomy Jurament (Mar 2, 2009)

This is one of those things that I just can't get that worked up about.  I don't have a problem with BAB.  I don't have a problem with THAC0.  Heck, I don't even have a problem with "look at the chart on the screen or on your character sheet."  It just isn't a significant factor, for me.

That said, one thing I like about the old AC system is that it allows some cool or interesting concepts about negative AC.  For example, AC0 might be considered a "break point," or "highest AC possible without magic," with negative AC being the result of magic.  Dave Arneson has used a rule where negative AC represents magic AC such that you need equal positive magic to overcome it; that is, if a monster has a -2 AC, you need a +2 weapon in order to damage it. 

One thing I find interesting is that in the original D&D LBBs, your PC's armor class was an actual _class_, and it indicated the kind of armor you wore.  Dexterity doesn't modify AC, and magic armor doesn't either -- it subtracts from the enemy's "to hit" roll.  

(Robert Fisher writes about some THAC0 approaches, here.)


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## Philotomy Jurament (Mar 2, 2009)

Hussar said:


> The numbers in 3e and 4e are such that limiting yourself to a range of AC's from 10- -10 just doesn't work, and once you get beyond those AC's, THAC0 become much more difficult to use.



That's a good point;  the numbers and scale in the WotC editions is much inflated, compared to early D&D.  (I found the larger numbers involved as levels went up in 3E to be off-putting, BAB or not, but I can see how BAB would be a little easier than THAC0, in those situations.)


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## Runestar (Mar 2, 2009)

THAC0's explanation always seemed a little weird to me.

The lower your AC/THAC0, the better. You want to roll high, but your final attack value must be lower than your opponent's AC for you to hit. 

It is a piece of cake once you have it all figured out, but that is just a layer of confusion which was never needed in the first place. I still remember my puzzlement when in Planescape: Torment, I saw my AC decrease when I had the nameless one wear that ring of AC+2, finding that I couldn't remove it as it was cursed, and thinking "crap, did I screw up?", despite the ring's entry stating it was supposed to be a boon.


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## Fifth Element (Mar 2, 2009)

Thondor said:


> I do admit that understanding how THAC0 functions is slightly more difficult conceptually. However, it more then makes up for it in accelerating game play.



I'll disagree and I'll tell you why. THACO is faster...for the players. Because it puts more of the maths on the DM. The player may only need to know what he rolled, and tell the DM, but the DM has to know both the target's AC and the attacker's THACO. Moreover, he has to know the THACOs of all the players at the table. If the players do the math on their attacks, it should be less time-consuming because they only have to worry about their own attack bonuses, as opposed to the DM needing to know the THACOs of everyone at the table. Players learn their own attack bonuses very quickly. The DM has other things to worry about than commit the party's THACOs to memory.


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## Keefe the Thief (Mar 2, 2009)

I´ll always remember the times when i tried to explain a prospective player how to compute his AC

"And i get a +1 Shield? Cool! Can i improve my AC by 1?"
"No, you improve it by two. So you lower it by two."
"What? Hm. Okay, i have AC 6 then. People have to roll 1-6 to hit me, haha!"
"No. It depends on the interaction between your AC and their THACO if they hit you."
"Hey DM, do the Bracers of Defense AC 6 set my AC to 6? And i want to use a shield, too!"
"No, they only set your AC to 6 if you have a natural AC of ten. If you have a Dex-Bonus to AC, you have to take that into account."
"Um. So i have AC 6, add a bonus to AC 7..."
"No, subtract a bonus for AC 5."

Note that we are talking German here, and using the even "prettier" acronym ETW0 - Erforderlicher Trefferwurf für Rüstungsklasse Null.


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## FireLance (Mar 2, 2009)

Hussar said:


> Player:  Hey, I have a THAC0 of -27, I roll a 14, I guess I hit an AC of minus 51.  Do I hit?



If you have a THACO of -27 and you roll a 14, you hit an AC of -41, not -51. 

I assume that wasn't a deliberate error to make a point?


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## S'mon (Mar 2, 2009)

Chaos Disciple said:


> Sorry if this is a little off topic
> 
> 
> 
> ...




No, I used it to mean the number you need to roll to hit, which for 3e = AC.

Edit: I find it much easier if the target number is determined before the roll is made.  THAC0 only works for me if it includes all bonuses so you can determine the target number, then roll an unmodified d20.

I don't find subtraction harder than addition.  I find small numbers easier than big ones.  Different people's (and peoples') brains work differently, and this explains the THAC0 controversy - for some it's a nice easy system, for others it's incomprehensible.


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## S'mon (Mar 2, 2009)

Fifth Element said:


> I'll disagree and I'll tell you why. THACO is faster...for the players. Because it puts more of the maths on the DM. The player may only need to know what he rolled, and tell the DM, but the DM has to know both the target's AC and the attacker's THACO. Moreover, he has to know the THACOs of all the players at the table. If the players do the math on their attacks, it should be less time-consuming because they only have to worry about their own attack bonuses, as opposed to the DM needing to know the THACOs of everyone at the table. Players learn their own attack bonuses very quickly. The DM has other things to worry about than commit the party's THACOs to memory.




As GM, I find 3e's "players handle attack resolution" much harder, because it forces me to be consistent in my terminology!  This comes up a lot with firing into melee and cover - is it -4 to hit, or +4 to AC? Has the player deducted it from their roll?   Often I miscommunicated and the player was deducting 4 while I was adding the same 4 to the target AC.  (It's a bit better now the PCs have Precise Shot).  I found 1e much easier where I determined the target number and the player simply rolled a d20 against it.  

I find the 3e+ system puts an extra burden on both the player, who has to calculate correctly each roll, and on the GM, who has to communicate correctly with the player.


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## Beginning of the End (Mar 2, 2009)

Thondor said:


> With THAC0 the name itself says it all. If you have a THAC0 of 17, you must roll a 17 to hit a Armor Class of 0.




No it doesn't. "You have to beat X to hit armor class 0" is just as legitimate as "you have to roll X to hit armor class 0". The phrase "to hit armor class 0" does nothing to distinguish between the two cases.



> 2. _Ease of Use. _A character who had a BAB of +5 would have a THAC0 of 15. Compare
> A 3e character with a BAB of +5 tries to hit a enemy with a AC 15. Player rolls a 7, (ummm 7 plus 5 is 12) hey DM I got a 12.  DM you miss. Next round, Player rolls a 13, (umm 13 plus 5 is uh 18), hey DM I got a 18. You hit. Next round, player rolls a 8 (umm, 8 plus 5 is 13), hey DM I got a 13. DM you miss.
> A  pre-3e character with a THAC0 of 15 tries to hit an enemy with a AC 5.
> Player rolls a 7. Player says "7", DM says "you miss". (The DM knows that no one around the table has a THAC0 better then 14.)




Wow. Talk about your blatant apples-to-oranges comparison. You could just as easily argue that the 3rd Edition DM should know that no one at his table has a BAB of +11.



> With THAC0 you figure out what number you need to roll on the die once. With BAB you roll the dice, add your modifier, and compare it to the target number . . . every single attack.




This argument has a bit more traction. But (and this is an important but) it only matters if the DM announces the AC when combat begins.

If the DM doesn't announce AC when combat begins, you have dramatically increased the bookkeeping the DM has to perform: They must now keep track of (or ask for) the THAC0 for each character; perform a calculation for the AC of each creature in the combat; either record them or repeat the calculation each time the PCs attack; and then do the comparison between the number rolled and the calculated to-hit number.

In 3rd Edition, all of this record-keeping and calculation has been off-loaded to the players. They tell them their result, the DM compares it to the monster's AC, and that's it.

More importantly, nothing about the BAB system prevents the calculation of a to-hit number once the target AC is known. (AC - attack bonus = to-hit number) Quite a few players at my 3rd Edition table do precisely that.

But note the key phrase there: "once the target AC is known"

This is the fundamental flaw with THAC0: In order to calculate a to-hit number, you need to perform a calculation using a piece of information that the attacker has (BAB or THAC0) and a piece of information that the defender has (AC). (In the BAB system, by contrast, the default calculation is performed on two pieces of information held by a single person -- the attacker. In both systems the result needs to be compared to a third piece of information.)

The other problem with THAC0 is confusing nomenclature of descending AC in which a + is sometimes a penalty and sometimes a bonus.

So the BAB system performs just as well as THAC0 does in a situation where a to-hit number can be calculated by the player. And it performs better than THAC0 does in a situation where the player cannot calculate the to-hit number (because AC is unknown). And it eliminates the confusing nomenclature of descending AC.



S'mon said:


> I agree - this does make THAC0 easier to use, where AC is known. You can do the same with ascending AC by deducting your attack bonus from the AC to get target number, but it's less intuitive.




How is

AC - BAB = target number

any more or less intuitive than

THAC0 - AC = target number?



S'mon said:


> As GM, I find 3e's "players handle attack resolution" much harder, because it forces me to be consistent in my terminology! This comes up a lot with firing into melee and cover - is it -4 to hit, or +4 to AC?




Umm... you are aware that AD&D *also* featured bonuses and penalties to BOTH attacks and armor class, right?


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## Korgoth (Mar 2, 2009)

I guess I really am a genius. I never found THAC0 confusing in the slightest, even as a child.

Maybe you guys just don't do subtraction enough. I'm sure you could get better with practice.


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## wedgeski (Mar 2, 2009)

THACO represents to me a lot of broken-ness about pre-3e D&D, namely the inconsistent directions in which stats improve. BAB represents the opposite. BAB wins in this humble gamer's opinion.


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## Nymrohd (Mar 2, 2009)

I remember trying to explain AD&D to friends back in high school. I lost most of them at THAC0.


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## S'mon (Mar 2, 2009)

Beginning of the End said:


> Umm... you are aware that AD&D *also* featured bonuses and penalties to BOTH attacks and armor class, right?




Yeah, but to me it was all just mods to the target number.   I never modified the attack roll (always a straight d20 roll), just the number needed to hit.  I'm aware now that that is not strictly by the book - obviously I always did '20 hits' since the 6 repeating 20s in the 1e DMG don't make sense on this approach.

Anyway, my point was that different brains work differently.  Yours clearly works differently than mine.

And incidentally, I'm finding that for online chat based play, ascending AC and d20+bonus to hit works much better, because the online dice roller already calculates the result of the d20+mods for me.  I've been using both C&C (ascending AC) and Labyrinth Lord (descending AC and THAC0 or tables) in Dragonsfoot chat games, and C&C is far far easier to run in that environment.


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## Nikosandros (Mar 2, 2009)

Korgoth said:


> I guess I really am a genius. I never found THAC0 confusing in the slightest, even as a child.
> 
> Maybe you guys just don't do subtraction enough. I'm sure you could get better with practice.



I'm fairly good at subtractions... it's just that I'm even faster at adding.

I'm a huge AD&D fan; for me, "true" D&D (for an appropriately restrictive definition of true) had descending AC.

That said, I really couldn't argue that THAC0 is more "logical" than BAB. I have no trouble using it, or doing table look-up (which is necessary, if you use the repeating 20s rule). I've never considered switching to ascending AC in AD&D, but I must say that BAB works just as well and I would also never dream of switching 3e or 4e to descending AC.


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## Raven Crowking (Mar 2, 2009)

Korgoth said:


> I guess I really am a genius. I never found THAC0 confusing in the slightest, even as a child.
> 
> Maybe you guys just don't do subtraction enough. I'm sure you could get better with practice.




Indeed.

I prefer positive AC (although not exactly BAB), and it is what I am using in RCFG.  I prefer positive AC because it is easier to explain, initially, although negative AC includes forcibly within it the obvious "tipping point" for armour where the DM should begin to exercise some caution.  Positive AC can lead to serious numbers inflation, if not checked, simply because the inflation is less obvious than in negative AC.

Also, I have never met anyone in real life who was unable to grasp either THAC0 or BAB.


RC


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## vagabundo (Mar 2, 2009)

THAC0 was always a barrier to my more casual players, they would look on in puzzlement as I figured it out for them. It definitely didn't speed up my games, it was a hindrance. 

I think the measure of it was how quickly I forgot how to do it after I switched to BAB.

And most people can add quicker than they can subtract in my experience.


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## Remathilis (Mar 2, 2009)

Raven Crowking said:


> Also, I have never met anyone in real life who was unable to grasp either THAC0 or BAB.




FWIW, the only people I ever met who never got Thac0/Downward AC were typically casuals (girlfriends, interested siblings) who barely got the basics of what an RPG is, let alone its mechanics. While 3e tended to overwhelm in other areas, I don't think I met too many casuals who didn't get "add roll X to bonus Y and tell the DM" while plenty lost it at "what am I subtracting from what again?"

For anyone who actually stuck with and learned the game though, Thac0 could be grasped.


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## Obryn (Mar 2, 2009)

Would now be a good time to point out that THAC0 doesn't even work in by-the-book 1e?

Those repeating 20's will catch you up every time.

-O


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## Reynard (Mar 2, 2009)

Never m ind THAC0 -- just use the combat matrices.  There's a good solid reason why those tables weren't in the PHB in 1E -- it's the DM's job to adjudicate, which includes combat.  When a character makes an attack, the player's job is to give the DM a total ("I rolled a 17!") and the DM's job to relate what happens ("Your sword stabs for his throat but he raises his shield just in time and you leave him with merely a nasty cut on the cheek.") I believe it was B/X that actually had the DM rolling for damage (though the player rolling for damage isn't a bad thing -- but i would suggest doing so simultaneously with the attack roll).

The same goes for saving throws in the "old school". The DM knows what save is required and what counts as a successful save.  All the player has to do is roll the die and tell the DM what he got. The DM informs the player that he was turned to stone, dropped off the ledge and shattered into 1000 pieces.

And before anyone screams control-freak DM, there's a real, player benefit reason to do this: every time the player has to look at his character sheet and add modifiers or look at the battleboard and count squares, that player is pulled out of the game. He's no longer thinking "Rath is pissed! That hobgoblin is going down!" He's instead thinking "If I move over here and get a flanking bonus, then I can power attack for 4 points and still have a 75% chance of hitting his AC." While the latter is wrong or bad, IMO it is less fun.


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## Obryn (Mar 2, 2009)

FWIW, I adapted a pseudo-BAB for my 1e game.  Mathematically, it works identically to the tables, but it front-loads the math.  I wanted to run as close to BtB as possible, but found that applying combat modifiers to the target's AC (rather than to the die roll itself) broke my brains.

(1a) For Fighters/Rangers/Paladins, take (Level-1).
(1b) For all other classes, look at the AC 10 row on the chart and find 10 minus this number.  (So, for a wizard, this would be -1 at 1st level.)

(2) Add all other bonuses from strength/dex, magic, and specialization.  This gives your Combat Bonus.

(3) In combat, roll a d20, add your Combat Bonus.  A roll of 20 counts as a 25, to replicate the repeating 20's on the tables.

(4) Behind the screen, I quickly add the monster's AC to this number.  If it equals or exceeds 20, it's a hit!

Monsters are even easier at low levels.  I just add their hit dice to the d20 roll, rounding up a hit die if they have from +1 to +3 extra HPs.  (And more dice if they have more.)

Then, I can put away the tables while preserving the combat math of 1e.

-O


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## Filcher (Mar 2, 2009)

I hope this thread lives for a long, long time ... 3.5 and 4E fans united!

So tell me more about this Thahcoe.


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## Sir Brennen (Mar 2, 2009)

I think the argument isn't that THAC0 and BAB calculations are mathematically equivalent isn't really the point.  It's the _basic premise_, the starting parameters, of THAC0 that initiates confusion in some players. Start at 10 and _decrease_ my AC value as it gets better?  And I can go negative? Whaaa?

I'm sure this has its roots in some wargame resolution table. But just the idea that "increasing the amount of protection I'm wearing" = "an increase in the value of the number that represents the amount of protection I'm wearing" is a straight-forward, intuitive approach. For THAC0, many people get stuck on "why does it work that way?"

And boiling down the comparison to THAC0 vs. BAB ignores the fact that these are both integral parts of their respective game systems, and additional confusion was caused by the way THAC0 worked with respect to the rest of the system. I add my Strength bonus and magic weapon bonus to my attack roll but subtract my Dex bonus and magic armor bonus from AC. So a bonus is a subtraction... except when it's not? You need me to make a Str check? Okay. 20! Awesome! What? I blew it? I thought 20 was the best thing you could roll?

With 3E and beyond, there's no need to mentally switch gears (or dice) when going from Saving Throws to Attacks to Hide in Shadows to Attribute Checks. This fact means that overall, 3E should play faster. However, in practice, I think that it then occasionally loses some momentum due to the many additional bonus/penalty/options which crop up in play that didn't in previous editions, which players and DM alike need to track.


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## Mallus (Mar 2, 2009)

Reynard said:


> He's no longer thinking "Rath is pissed! That hobgoblin is going down!" He's instead thinking "If I move over here and get a flanking bonus, then I can power attack for 4 points and still have a 75% chance of hitting his AC."



The people I game with have no trouble thinking both thing simultaneously, or at least, can effortlessly switch between _player_ and _character_. 

This has the added benefit of allowing the DM to be completely transparent about the mechanics ("It's REF defense is 19") and thus off-loading some of the crunch-work to the players.

Oh, and good riddance to THAC0!


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## Reynard (Mar 2, 2009)

Mallus said:


> The people I game with have no trouble thinking both thing simultaneously, or at least, can effortlessly switch between _player_ and _character_.




I'm doubtful, but I'll take your word for it. 



> This has the added benefit of allowing the DM to be completely transparent about the mechanics ("It's REF defense is 19") and thus off-loading some of the crunch-work to the players.




I am not sure this is a benefit -- or, rather, I am not sure the benefits outweigh the costs.


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## avin (Mar 2, 2009)

THAC0 is the worst idea ever made for D&D.


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## kitsune9 (Mar 2, 2009)

Thondor said:


> There has always been a rhetoric on these boards that discredits THAC0 (To Hit Armour Class 0) as being by far inferior to BAB (Base Attack Bonus). Posters state this as a matter of course, saying things like the adjustement to BAB (from THAC0) was so inherently logical that it is stunning that it didn't happen earlier.




I didn't have a problem with THAC0. I thought it worked for our group fairly well when we played the earlier editions.

The one thing that worked well for me was to avoid cheating. When we figured out a PC's THAC0 to be 13, then whatever he rolled off the die, I knew if he hit or not, but when I had players who "insisted" on adding their modifiers, every die result was always in the mid-20's and characters were only 4th or 5th level. Needless to say, we got rid of the couple of players who did this.


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## Puggins (Mar 2, 2009)

Thondor said:


> Here's me explaining THAC0: the number you roll >= THAC0 - AC
> 
> Here's me explaining BAB: the number you roll + BAB => AC




Thondor, with all due respect, you're ignoring that both equations are commutatively equal.

X >= THACO - AC  *:*  X + AC >= THACO

X >= AC - BAB  *:*  X + BAB >= AC

They are the same in terms of mathematical functionality.  The difference lies in their level of intuitiveness.

Look at the the second equation of each.  

The BAB equation is perfectly intuitive.  I have a value that tells me how good I am at swinging a sword.  If I add that value to the die roll, which also tells me how well I swung at this very moment, I get the sum total of the effectiveness of my attack.  If it's higher than a target number, then I hit.

The THACO equation... welll, it's just as workable, it is simply less intuitive.  I have to add the target number I'm trying to hit to my roll, and then comparing the total against my skill representation.  The first version of the equation is somewhat more intuitive, but not increidbly so- you have the monsters AC, which gets better as it goes down compared against one value that gets better as it goes down and another value that gets better as it goes up.  It's simple, but it's not elegant.

That said, all brains are wired differently.  If you really like THACO, then converting 3/4e to THACO is amazingly simple:

AC(THACO) = 20 - AC(BAB)

THACO = 20 - BAB

I don't particularly care for it, since I prefer a system that goes one direction  in nunber quality, but it's ultimarely your game.


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## Fifth Element (Mar 2, 2009)

S'mon said:


> Yeah, but to me it was all just mods to the target number. I never modified the attack roll (always a straight d20 roll), just the number needed to hit. I'm aware now that that is not strictly by the book



Fair enough, but note the "to me", and the fact that you could do the very same thing in 3E. Any modifiers other than the character's basic bonuses could be applied to AC instead.


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## Dragonhelm (Mar 2, 2009)

Personally, I think the d20 designers should have kept the term THAC0 around, even if it didn't make sense.  I mean, it just sounds cool.  At least name a character Thaco.  

Or maybe put it in as a secret organization in d20 Modern - T.H.A.C.O.

Okay, I got nothin'.


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## Storminator (Mar 2, 2009)

The problem with ThacO calculations is they require the roll, the modifiers, the Thac0 number itself, and the AC. Without advance prep work (i.e. the DM collects Thac0 and attack modifiers for all players), neither player nor DM has all this information.

Therefor, to get to the decision of whether or not you hit requires either 1) the player to give this info to the DM in pieces (I rolled a 12 with modifiers, and my Thac0 is 11) and then the DM does the math on the fly or 2) the player does all the math up front and hands it to the DM (I hit AC -1 or better). Case number 1 bottlenecks all the math at the DM, and case number 2 is just BAB calculations only with subtraction and an extra step. In either case BAB calculations are superior.

And those are optimum cases. IMX, less than optimum is what happens. 
One guy is perfect (I hit AC -1 or better)
 one guy always forgets to add his modifiers until after he's told he misses, then adds in his modifiers (I got an 11 and I have a Thac0 14. I miss? Oh, I have +2 STR and a magic weapon...)
 one guy doesn't do anything (player:I rolled a 9, I have +3 to hit DM: what's your Thac0? Player: where is that written again? oh yeah, it's 13. No wait! I leveled up, what's my Thac0 now? what class am I? Does it get better this level?)
and one guy thinks he knows what he's doing, but always screws it up (I hit AC -6 or better... all night long...)

I played some Hackmaster after years of 3e, and every frikkin session was like that last paragraph. My degree in applied math was screaming the whole time... 

PS


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## justanobody (Mar 2, 2009)

Lanefan said:


> I've been running 1e for 25-odd years and still haven't figured out THAC0.  To me, it just adds an unnecessary layer of complication - I don't care whether a swing hits AC 0, I care whether it hits the specific AC of the particular opponent at the time - all I want to know is whether the base roll, bonuses, penalties, fight level, and AC end up adding to 21 or more.  THAC0 doesn't help me there, and instances of both the target's AC being 0 and the attacker's listed THAC0 rating being accurate for the situation happen rarely enough that I'm not going to waste the time checking.
> 
> Lanefan




THAC0 just converts all the tables into a simple formula to create a number line

-1 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10

THAC0 is at the zero on this line.

say THAC0 12

put down the number 12 under or over the zero on the character sheet. Forget which one has the THAC0 line on it, but you can make it yourself.

Then write down the numbers along the rest of the line. It is elementary school math.

AC 1 moves one place along the line so it changes THAC0 by one. gives you one better to hit that AC with. Instead of needing 12, you only need 11 to hit AC 1.

AC basically is your modifier to hit when comparing to AC0.

With the line you dont need to tell the DM anything or him to do any math.

You roll a 10 with THAC0 12, you can hit AC 2.

Got weapon or other bonus, then add it to the dice roll. Got a penatly, then take it away from the dice roll.

+4 weapon makes your roll a 14. looking at the number line then you 10 became a 14 so you could hit an AC -2.

Same as BAB, just with THAC0 there is a greater chance to hit things in the long run wherein BAB allows for ACs that you could never hit.

All math is just addition.

Addition = ....addition
Subtraction = adding the negative
Multiplication = adding something to its self a number of times
Division = adding a part rather than a whole of something to something else.

The reason you want to know what it takes to hit AC0 is for the mid range of the entire AC range.

BAB makes certain ACs useless. Why start at 10? Why not start at AC0?

Because you would have things that could never be missed unless you impose a critical fumble rule. I don't care who you are, I have seen all kinds of people swing and ax and MISS a tree.

At least THAC0 doesn't waste parts of its range, and is a simple formula.

DM uses:
THAC0 - AC = # needed to hit (dice roll + modifiers)

Player uses:
THAC0 - (Number rolled + modifiers) = AC you can hit

pick one.

using the player one and the previous THAC0 of 12 and the +4 weapon/whatever bonus.

12 - (10+4) = -2
12 - 14 = -2

yup. it works

using the one for DMs

12 -(-2) = 14
12 + 2 = 14

With a THAC0 of 12 you need a 14 to hit a AC -2 whatever.

So if you dont know the AC it doesnt matter. THAC0 works for both player and DM. It is just most commonly expressed form the DM perspective where he known the AC needed rather than given what the players would need to tell the DM.

For all that care, not just you that is.

And as previously mentioned, sooner or later you will learn the AC no matter which method you use. BAB or one of the THAC0 formulas. Then you can just use the DM formula to figure out what you need to roll, and what to attack with.


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## billd91 (Mar 2, 2009)

avin said:


> THAC0 is the worst idea ever made for D&D.




Oh, no it isn't. In its day, it was a brilliant refinement allowing the DM to not have to look at attack tables all the time. And it did away with the repeated 20s on attacks, each of which could be matched with to hit modifiers and some of which had to be natural 20s.

That said, there was no real reason to continue on with the wargame-roots of combat adjudication after 2e (or even in 2e). So it was another good refinement to just flip the math around and grow AC rather than reduce it as it improved.


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## Mallus (Mar 2, 2009)

Reynard said:


> I'm doubtful, but I'll take your word for it.



Do you think it's that uncommon for people to be able to experience the rules of the game and the fictional world of the game at the same time, without one interfering with the other? The ability to do that sounds like a _requirement_ for enjoying role-playing games.  



> I am not sure this is a benefit -- or, rather, I am not sure the benefits outweigh the costs.



It's certainly a benefit when it comes at no cost (to the particular group).


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## billd91 (Mar 2, 2009)

justanobody said:


> BAB makes certain ACs useless. Why start at 10? Why not start at AC0?
> 
> Because you would have things that could never be missed unless you impose a critical fumble rule. I don't care who you are, I have seen all kinds of people swing and ax and MISS a tree.
> 
> At least THAC0 doesn't waste parts of its range, and is a simple formula.




Why start at 10? To balance the components going into attacking so that when the difference between an attacker's bonuses and a defender's bonuses = 0, the die generates a 55% chance to hit. Simple as that.


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## Mercule (Mar 2, 2009)

Lanefan said:


> I've been running 1e for 25-odd years and still haven't figured out THAC0.  To me, it just adds an unnecessary layer of complication



Generally agree.  While I've been playing 3e for most of its life, I've been playing D&D in some form since the early 1980s.  I found THAC0 to be a lousy, cluttering addition to 2e or late 1e.  I've never seen it's advantage, from either side of the screen, and the repeating 20s make the math more difficult than it is usually portrayed.  I've always used a DM screen, so I always have the attack tables in front of me -- which results in me actually being quicker at finding a hit/miss than any player has ever done the math for me.  Sure, the 2e character sheets had the row of boxes to write out the AC various die rolls would hit, but that's not using THAC0; it's just copying the table from the DMG.

I do think the BAB was one of the best changes in 3e and was glad to see them keep it in 4e.  I don't love it enough that I'd ever try to reverse engineer older editions, but I sure wouldn't use THAC0.

So, my opinion:

BAB >> to-hit tables >> THAC0


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## Obryn (Mar 2, 2009)

justanobody said:


> All math is just addition.
> 
> Addition = ....addition
> Subtraction = adding the negative
> ...



Is this really your argument?

"Subtraction is just as easy as addition, since subtraction is just adding a negative number."

"Multiplication is just as easy as addition, since it's just adding numbers a lot of times."

I think that's a rather specious argument that doesn't consider how an actual human brain deals with numbers.

-O


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## justanobody (Mar 2, 2009)

Runestar said:


> THAC0's explanation always seemed a little weird to me.
> 
> The lower your AC/THAC0, the better. You want to roll high, but your final attack value must be lower than your opponent's AC for you to hit.




Dave created the system based on naval vessel rqtings, where the lower number was better.

Think of it like spaceships vs watercraft, and underwater craft.

We live at 1 atmosphere. Spaceships must be built to survive 0 atmospheres.

Normal ships require 1 atmosphere to not be crushed under Earth's gravity.

So a spaceship can survive 1 and 0 atmospheres.
Watercraft can survive at least 1 atmosphere.
Underwater craft can survive 1 atmosphere, 2 atmospheres, etc as they can go deeper.

The ratings i think go negative to show how far below sea level a vessel can travel before it reaches crush depth.

so a -1 rating would mean it can withstand twice normal atmospheric conditions or 32.x PSI from the outside.

Which is what a hit is in regards to damaging something. Pressure from the outside needed to cause damage.

So something with a -2 rating could take more pressure before being damaged than something with a 1 or -1. Thus THAC0 and its use of lower equals better.

Its what happens when smart people make games with technical backgrounds.

You could always rewrite THAC0 and have the numbers go up. that is all BAB did. same sytem, just different window dressing.

But i hope that explains a bit why the lower numbers were better with THAC0. maybe on of the Dragon Magazines gives it in better detail. Check that thread to see if it has been mentioned yet by un in "reading the entire run".

So all in all the main problem with the THAC0 system, is people just get caught up on the math. All there is to it.

So for anyone having problems with THAC0, just use the one for the players that simple algebra lets you extract that i gave above, and will repeat here:

Player uses:
THAC0 - (Number rolled + modifiers) = AC you can hit

And let the DM do the comparisons.

player number =< AC of target means a successful hit.


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## Reynard (Mar 2, 2009)

Mallus said:


> Do you think it's that uncommon for people to be able to experience the rules of the game and the fictional world of the game at the same time, without one interfering with the other? The ability to do that sounds like a _requirement_ for enjoying role-playing games.




Many years, many people and many game systems tells me that few, if any, people do each in equal measure, and that the system in question has the largest effect on which aspect is prevalent at any given moment (though individuals' experience level with a particular system will also have an impact). Basically, when calculations or rules/sheet referencing is required during play, immersion suffers.  Note that this has nothing to do with _role-playing_ -- immersion is a completely separate issue and one i think has a far greater impact on the final "fun" quotient.

In short: yes, I think it is uncommon for people experience the rules of the game and the immersive aspect of play in equal measure.


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## Filcher (Mar 2, 2009)

justanobody said:


> Dave created the system based on naval vessel rqtings, where the lower number was better. [snip]




This was an awesome history lesson.


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## justanobody (Mar 2, 2009)

Obryn said:


> Is this really your argument?
> 
> "Subtraction is just as easy as addition, since subtraction is just adding a negative number."
> 
> ...




The human brain is a moot point.

Math is math.

2 + 2 will always equal 4 in a base10 system.
2 -(-2) will also always equal 4 in a base10 system.

My arguement was the way people look at THAC0. Again se the Player one presented and you get the same math, but a different variable. It just takes the algebra to manipulate the equation to get what you need.

A - X = B

you have to solve for X so do it before you do the math.

You know you dont have X so solve for X.

A - X + X = B + X
Since X - X = 0 remove them from the left hand side

A - (-B) = B + X - B
Since B - B = 0 remove them from the right hand side

A + B = X

Now you just have to plug in the A and B to find your X that you dont know.

So rather than using a DM view of the formula, since he knows your THAC0 by asking, and knows the AC...

THAC0 - AC = # needed to hit (dice roll + modifiers)

The DM can tell you what you need to roll with your modifiers to hit.

Use the player view of what you know. Your modifiers, your THAC0, and what the dice gives you and tell the DM what AC you can hit.

THAC0 - (Number rolled + modifiers) = AC you can hit

Same equation, different looks at it depending on your knowns and the variables you have available to YOU.

Just depends on what you are trying to figure out.

You don't need a monsters AC to know what you can hit. You don't ever need to know it, but can figure it out. That was my point.

Since a list of monsters ACs are not provided in the PHB, you use what you know to determine what you can do. Heaven forbid someone creating something on their own and someone doesn't know its AC by looking it up in a published book! 

So like the rest of the game, take the information you have, and determine what to do with it. Don't trivialize over a chance to hit, just because of the math.

You have two doors to pick from. how do you know which one is the right door when you enter a room form a third door. You use what you know, or look for the right clues. You know the correct door isn't the one you entered from.

THAC0 gave you all the clues you needed represented in mathematical expressions.

So use the information given to figure out what you need to do. Be it with THAC0, BAB, or picking between those two unopened doors.


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## Obryn (Mar 2, 2009)

justanobody said:


> The human brain is a moot point.
> 
> Math is math.



When it's human brains - not computers - actually doing the calculations in real-time at the game table, it's _anything but_ a moot point.

As for the rest - I don't really know how it applies.  I know THAC0, and I know BAB.  I don't need a discussion of base 10 calculations.  As a real person and a DM, I'm concerned about two things:

(1) Numbers that are easy to grasp for real people, including casual gamers.
(2) Quick calculations at the table.

I think BAB and positive ACs fit criterion 1 perfectly.  "High is good" is the natural way peoples' minds work, and it fits in with their expectations.

Also, addition is quicker and more intuitive than subtraction for the human brain, so criterion 2 is fulfilled.

-O


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## Umbran (Mar 2, 2009)

justanobody said:


> The human brain is a moot point.
> 
> Math is math.




Oh, really?

There's a song by Tom Lehrer called "New Math".  It goes through the process of subtracting 173 from 342, in base ten and then base 8.

Folks who went through school from the 1960s and onward don't get what's so funny.  He's just doing arithmetic as we learned it.  The funny thing is that the folks who learned arithmetic earlier did it _differently_, such that during the transition (when the song was written), parents had difficulty helping their kids do their homework - the parents could get the same answer (because math is math), but confused their kids when they tried to show them how to get that answer, because the schoolteacher showed them something else.

You can, if you wish, go about the process of adding 19 and 1 via set theory, starting at the definition of the null set and working your way up.  But you'd not want to do that at the gaming table.  Rather cumbersome.  THAC0 is notably less cumbersome than set theory, but a bit more cumbersome than BAB.


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## justanobody (Mar 2, 2009)

Right. Bigger is better. How is your bag phone working for you now? How about that phonograph you carry your music around on to listen to?  Not to forget that 14 inch quill you use and ink pot to dip it in and the scrolls on which you write.

I have no idea what you do when you have a minotaur that just cant fit through a hole in a wall. Probably make the hole bigger rather than let the gnome or other creature go through it and unlock the door for everyone else.


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## Obryn (Mar 2, 2009)

justanobody said:


> Right. Bigger is better. How is your bag phone working for you now? How about that phonograph you carry your music around on to listen to?  Not to forget that 14 inch quill you use and ink pot to dip it in and the scrolls on which you write.
> 
> I have no idea what you do when you have a minotaur that just cant fit through a hole in a wall. Probably make the hole bigger rather than let the gnome or other creature go through it and unlock the door for everyone else.



I really don't know how this applies, unless you honestly don't understand human psychology and the way the human mind interprets numbers.

I know you want to make this an issue of pure math, but pure math gets distorted once you add people.  Human brains are not perfect computers; they exhibit tendencies and preferences.  If you ignore those tendencies and preferences, you end up with confusion.

-O


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## justanobody (Mar 2, 2009)

Umbran said:


> Oh, really?
> 
> There's a song by Tom Lehrer called "New Math".  It goes through the process of subtracting 173 from 342, in base ten and then base 8.
> 
> ...




I just see the same math, with an outrageous range with BAB. There are some thing you just cannot hit due to the unlimited range of BAB. It is the same system, but adds unneeded range to it. As you say the players get int he way of it all, and they do. Sadly players dont think about the unconstrained system of BAB having unlimited AC range, and they will gripe when they try to attack something that they cannot damage, and then die because they were given too much range to play with.

At least with THAC0 system you had a defined range. It wasn't as hopeless to try to attack something.

To me both systems are just math. simple and easy. take what you have and find out what you need to know.

That is it in a nutshell, no matter which method you derive to get your information from. If you dont like the equation, then just do as I did, and change it to one that works better for you. Don't get hung up on the math, or fear of subtraction or whatever.


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## justanobody (Mar 2, 2009)

Obryn said:


> I really don't know how this applies, unless you honestly don't understand human psychology and the way the human mind interprets numbers.
> 
> I know you want to make this an issue of pure math, but pure math gets distorted once you add people.  Human brains are not perfect computers; they exhibit tendencies and preferences.  If you ignore those tendencies and preferences, you end up with confusion.
> 
> -O




I am just saying 2+2 will not change to 5 just so Jethro is right. Jethro just has to accept that 2+2=4.

Everyone does not interpret number the same way either. Psychology tells you that people experience everything different from the next person. So the easiest way is the one that is common to all.

The math. Some people will prefer it presented to them one way, others the other, but it still boils down to the same math; or fear thereof.

When in doubt do like every other part of D&D. Ask someone else for help. You don't understand a spell, power, feat, NWP, then ask another player. You can't figure out THAC0 right, then ask another player. Don't get hung up on trivial crap to bog down the game. IF you don't like a game because you can't figure out some part of it that takes math you don't get, then don't play games that involve math.

I have never seen a game where a player had a problem with some part of D&D, and other players weren't ready to help. Don't try to under stand why smaller is better, it is just part of the game. Are you going to ask why fighters don't cast spells next? It also is part of the game. They weren't meant to. Learn to accept things even if you cannot fully understand them. The game is much more fun that way.

THAC0 works efficiently and easily.

That is all there is to it.


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## Stoat (Mar 2, 2009)

justanobody said:


> THAC0 works efficiently and easily.
> That is all there is to it.




Your explanations certainly demonstrate the simplicity and elegance of the thac0 system.


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## Sir Brennen (Mar 2, 2009)

justanobody said:


> Right. Bigger is better. How is your bag phone working for you now? How about that phonograph you carry your music around on to listen to?  Not to forget that 14 inch quill you use and ink pot to dip it in and the scrolls on which you write.



What. Are. You. Talking. About?

Straight-forward, simple and intuitive are better. More efficient is better. There's no such thing as "bigger" math. Only more complex, which THAC0 is -not the formula for applying it itself, an equine this thread has bludgeoned sufficiently, but the parameters of its variables, the opposed directional nature of AC vs attack role, which causes people to ask "Why is it like that? Wouldn't it make more sense for it to be this other way instead?." For an interactive, social game, if you're starting point isn't easily explained and grasped by a human mind, then it doesn't matter that "math is math" when it comes to a preferred method.


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## Raven Crowking (Mar 2, 2009)

The range issue is a real issue, because BAB doesn't tell you where the middle of the number line being used actually is.  Is it 20?  21?  25?  30?  THAC0 allowed a system to be designed around a set range of numbers; that is inherently easier than designing around an open range of numbers.

IMHO, many of the problems with 3e and 4e are caused by that open range of numbers, either directly or indirectly.  Certainly, that open range of numbers makes for a steeper power curve, and hence more difficult balance issues.

Even though I am a proponent of positive AC, in RCFG I've intentionally limited the power curve to model a more THAC0-like progression.  And mine is neither the first nor the only game to do the same.


RC


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## Obryn (Mar 2, 2009)

justanobody said:


> I am just saying 2+2 will not change to 5 just so Jethro is right. Jethro just has to accept that 2+2=4.



...who said it did?  This is neither here nor there.



> Everyone does not interpret number the same way either. Psychology tells you that people experience everything different from the next person. So the easiest way is the one that is common to all.
> 
> The math. Some people will prefer it presented to them one way, others the other, but it still boils down to the same math; or fear thereof.



Of course the math is the same either way.  The only argument is about what's easier and more intuitive.



> When in doubt do like every other part of D&D. Ask someone else for help. You don't understand a spell, power, feat, NWP, then ask another player. You can't figure out THAC0 right, then ask another player. Don't get hung up on trivial crap to bog down the game. IF you don't like a game because you can't figure out some part of it that takes math you don't get, then don't play games that involve math.
> 
> I have never seen a game where a player had a problem with some part of D&D, and other players weren't ready to help. Don't try to under stand why smaller is better, it is just part of the game. Are you going to ask why fighters don't cast spells next? It also is part of the game. They weren't meant to. Learn to accept things even if you cannot fully understand them. The game is much more fun that way.
> 
> ...



So rather than take a fairly simple construct that people find easier to understand, you suggest we take the more complex construct because people can just ask for help with it?

And if you don't like THAC0, you're better off playing something else?

I don't think you're helping your case here.

-O


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## Mercule (Mar 2, 2009)

justanobody said:


> The human brain is a moot point.
> 
> Math is math.



I have two ways to respond to this.

1) Correct.  Math is math.  THAC0 and BAB are essentially the same equation, just counting opposite directions.  Neither is superior to the other because math is math.  The entire discussion is pointless.

2) Incorrect.  While the universal rules of math are immutable and neutral, the advantage of BAB vs. THAC0 are about _ease of use_.  Ease of use is determined almost entirely by the human element.  Most people find addition to be quicker and easier than subtraction.  Therefore a system that minimizes subtraction has a better usability.  Between the two, BAB uses less subtraction.  Therefore, BAB is better.  QED.  There are other reasons, but that one is sufficient.

Basically, the best THAC0 can hope for is to be no worse than BAB.


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## Obryn (Mar 2, 2009)

Raven Crowking said:


> The range issue is a real issue, because BAB doesn't tell you where the middle of the number line being used actually is.  Is it 20?  21?  25?  30?  THAC0 allowed a system to be designed around a set range of numbers; that is inherently easier than designing around an open range of numbers.
> 
> IMHO, many of the problems with 3e and 4e are caused by that open range of numbers, either directly or indirectly.  Certainly, that open range of numbers makes for a steeper power curve, and hence more difficult balance issues.
> 
> ...



I just want to note for clarity that the range issue is a completely separate one from THAC0 vs. BAB.

It's conceivable to use THAC0 with ACs that range from -80 to 10, or even from -100 to +100.  This would be inane, but the THAC0 system doesn't inherently prevent this.

On the other hand, it's also conceivable to limit ACs with a BAB system to a 10 to 30 range, offering the same value spread as traditional THAC0.

I'm sure you get this, RC, but some other folks on this thread might think these are inextricably linked and I want to clarify.

-O


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## Daniel D. Fox (Mar 2, 2009)

To hack-o, no thanks!


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## billd91 (Mar 2, 2009)

Raven Crowking said:


> The range issue is a real issue, because BAB doesn't tell you where the middle of the number line being used actually is.  Is it 20?  21?  25?  30?  THAC0 allowed a system to be designed around a set range of numbers; that is inherently easier than designing around an open range of numbers.
> 
> IMHO, many of the problems with 3e and 4e are caused by that open range of numbers, either directly or indirectly.  Certainly, that open range of numbers makes for a steeper power curve, and hence more difficult balance issues.




I agree that you have a pretty important point here and I'd say it applies particularly strongly to saving throws and save DCs.
The open-ended range and stacking modifiers really sends things sprawling out at the higher end.


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## Sir Brennen (Mar 2, 2009)

Raven Crowking said:


> The range issue is a real issue, because BAB doesn't tell you where the middle of the number line being used actually is.  Is it 20?  21?  25?  30?  THAC0 allowed a system to be designed around a set range of numbers; that is inherently easier than designing around an open range of numbers.
> 
> IMHO, many of the problems with 3e and 4e are caused by that open range of numbers, either directly or indirectly.  Certainly, that open range of numbers makes for a steeper power curve, and hence more difficult balance issues.
> 
> Even though I am a proponent of positive AC, in RCFG I've intentionally limited the power curve to model a more THAC0-like progression.  And mine is neither the first nor the only game to do the same.



This is getting into a whole lot of other design issues, though. The inflation of BAB, AC and even saving throws has more to do with:

the way attribute bonus are distributed in 3E
the way attributes can be increased in 3E
the introduction of feats which give bonuses
the codification of all the other stackable bonuses (sacred, luck, enhancement, etc.)
the introduction of attributes for creatures, which will often have stats far in excess of PC norm, and can benefit from the same bonuses as PCs
Now, one could still calculate a maximum allowed AC/BAB for combatants in this system since there are defined caps for these other aspects of the game (+5 enhancement on magic weapons/armor, +6 on stat booster items, limits to stacking, max possible attribute at level X, etc). It's still going to be high, just given the breath of bonuses possible. But you could do it, and have a more THAC0'ish set range. However, that would mean setting an artificial limit on many other aspects of the game.

To me, there's nothing wrong with an open-ended system, especially since creatures of an appropriate CR should will have AC's within a range which is not impossible for the PCs to deal with. There are problems with the open-ended system as implemented in 3E, though, especially at higher levels.

I like that 4E has stripped out alot of the additional bonus types, and codified acceptable AC's for a given level (monsters still have stats, but their AC, HPs, etc. are less tied to them and more to the level they are being designed for.) In fact, there is a hard limit for monster AC's : A 30th level Soldier creature has a max of AC 46.


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## justanobody (Mar 2, 2009)

Obryn said:


> ...who said it did?  This is neither here nor there.
> 
> 
> Of course the math is the same either way.  The only argument is about what's easier and more intuitive.
> ...




Going back tot he psychology of it you neglect that for osme all those extra parts even if just addition add unneeded complexity.

BAB +modA +modB +modC +...and so on for all the feats, and other places where bonuses come from. So for them how does the BAB approach make it any easier?

It still boils down to if you don't get it then ask someone else rather than complain that you dont get it. Try taking remedial math classes if you must get it, or don't complain to other people because you just dont get it, whatever IT is.

I have seen someone get plain out frustrated with the number of modifiers in 3rd that they wanted to quit. The DM just asked if anyone would mind figuring it up for the player each time. Everyone offered. The player got to play without fusing with the crap they didnt like, and everyone was happy. No loss to the game.

Oddly enough each group already has at least one person like this who has already got everyone modifiers BAB/THAC0 already figured up for them and ready to go that I have seen. Find that peson and ask them.

Work smarter not harder. In the case of dealing with numbers, if there is someone better at it, then let them do it if they are willing. If you are bogging down the game with either system, then you have to change your approach to how you play it.

Do it all before hand rather than on-time calculations. Which comes back to the character sheet that already had the number line on it. Just find the thing you have and read what you can do.

I so miss the tables. People need to use them more often for this very reason. Do you math before the game NOT during it.

The THAC0 system goes from -10 to 10. that is its range. Read a DMG and PHB to find this out.

Pigs could fly if you want them to, but it is not a part of the system. Everything in THAC0 including monsters were written under the understanding the best AC was -10, the worst was 10.

What you do to alter that, you must balance the whole game against. Thus the BAB system can easily break itself under the weight of the constantly increasing range with no limit.


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## Obryn (Mar 2, 2009)

justanobody said:


> Going back tot he psychology of it you neglect that for osme all those extra parts even if just addition add unneeded complexity.
> 
> BAB +modA +modB +modC +...and so on for all the feats, and other places where bonuses come from. So for them how does the BAB approach make it any easier?



The number of modifiers is another completely separate issue.  It has absolutely nothing to do with THAC0 vs. Attack Bonus.

For attack bonuses, you just calculate them ahead of time.  For THAC0, you just add/subtract from your THAC0 ahead of time.

And situational modifiers are always situational, no matter which system you're using.



> It still boils down to if you don't get it then ask someone else rather than complain that you dont get it. Try taking remedial math classes if you must get it, or don't complain to other people because you just dont get it, whatever IT is.
> 
> I have seen someone get plain out frustrated with the number of modifiers in 3rd that they wanted to quit. The DM just asked if anyone would mind figuring it up for the player each time. Everyone offered. The player got to play without fusing with the crap they didnt like, and everyone was happy. No loss to the game.



Again, the number of modifiers is a completely separate issue.



> Work smarter not harder. In the case of dealing with numbers, if there is someone better at it, then let them do it if they are willing. If you are bogging down the game with either system, then you have to change your approach to how you play it.
> 
> Do it all before hand rather than on-time calculations. Which comes back to the character sheet that already had the number line on it. Just find the thing you have and read what you can do.
> 
> I so miss the tables. People need to use them more often for this very reason. Do you math before the game NOT during it.



...again, I don't see how this applies.  And, I don't see how it's a feature of the system.  If you don't gain anything from increased complexity, it's complexity for complexity's sake.



> The THAC0 system goes from -10 to 10. that is its range. Read a DMG and PHB to find this out.
> 
> Pigs could fly if you want them to, but it is not a part of the system. Everything in THAC0 including monsters were written under the understanding the best AC was -10, the worst was 10.
> 
> What you do to alter that, you must balance the whole game against. Thus the BAB system can easily break itself under the weight of the constantly increasing range with no limit.



1e and 2e limited the range from -10 to +10.  That's completely separate from what is or isn't possible using THAC0.

I could, using an attack bonus system, limit my ACs to a range of 10 to 30.  (In fact, many people who run 1e/2e using positive ACs and attack bonuses do just this.)   

I could, using a THAC0 system, limit my ACs to -20 to +15.  Or from -5 to +9.

In both cases, these ranges and limits are not inherent mathematical features of either system - they are game conventions set up by entirely different rules.

_They are separate arguments.  An argument for limited range is not an argument for THAC0.  An argument for unlimited range is not an argument for Attack Bonuses._

-O


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## Raven Crowking (Mar 2, 2009)

Obryn said:


> I just want to note for clarity that the range issue is a completely separate one from THAC0 vs. BAB.




While it is true that, as you say, "It's conceivable to use THAC0 with ACs that range from -80 to 10, or even from -100 to +100", it is also true that the issue is not completely separate.  

This is true for two reasons:

(1)  In relation to the much argued about human cognition, AC 0 is automatically significant, whether or not the system extends to 100 and -100.  The system, by its very nature, tells you where the "center point" it balances upon is.

(2)  Related to the above, when you set the worst high AC, the "center point" automatically suggests the best low AC.  Thus, in the system as presented, the worst AC is 10, and the best AC is -10.

Both of these factors make game balance inherently easier to achieve.  As 3e's out-of-control spiral amply demonstrates, IMHO, removing a known "fulcrum point" also removes any useful sense of simulated scale.  It quickly ceases to become obvious where, on a continuum, a certain value should lie.  This is even more true in 4e, IMHO, where the numbers used no longer map to any meaningful simulation at all.  

If the math is co-equal, then there are two human variables to consider:  

(1)  Is this easier to use at the table?, and

(2)  Is this easier to use when designing new materials?

I think that BAB wins on (1), and THAC0 wins on (2).  OTOH, as I suggested earlier, I think that it is possible to related BAB to THAC0 strongly enough to compensate somewhat (but not entirely) on (2), which is what I am attempting with RCFG.

While, as I said before, I prefer BAB, I don't find it a completely correct statement to say that BAB is easier than THAC0 overall.  It is just easier than THAC0 for some specific tasks.  And THAC0 is easier than BAB for some others.



> I'm sure you get this, RC, but some other folks on this thread might think these are inextricably linked and I want to clarify.




Fair enough.

OTOH, you should also clarify that your clarification doesn't relate to the THAC0/BAB paradigms in any edition of D&D to date, whereas my point that you are clarifying does.   


RC


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## justanobody (Mar 2, 2009)

Obryn said:


> Again, the number of modifiers is a completely separate issue.




Prove it.

Using 1st, 2nd, 3rd, and 4th.

Provide each equation with EACH possible modifier to derive a to-hit number for each system.

Feel free to use my previous example as a starting point and expound on the various modifiers therein for each system.

THAC0 - (dice roll + modifiers) = AC able to hit

Create the formula for BAB etc and plug in ALL possible modifiers, and show me how it is a separate issue, or if the volume of modifiers in one system could not cause problems with that system sheerly by there quantity.


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## Raven Crowking (Mar 2, 2009)

Obryn said:


> The number of modifiers is another completely separate issue.  It has absolutely nothing to do with THAC0 vs. Attack Bonus.




Just to be clear, since it has come up from more than one angle:

The number of bonuses is directly related to the change from THAC0 to BAB.  When BAB opened up the range of numbers possible, the range of potential bonuses was likewise opened up.

In a system where there is a 1 in 10 base chance of success, no modifier can allow for more than a cumulative +9 bonus....at least not meaningfully.

Likewise, in the THAC0 system _*as it existed in D&D*_, no modifier could reduce AC below -10.  With a base AC of 10, it takes 20 steps to reach -10, and that means that the range of meaningful modifiers is 20.  This is a reason why, in general, there are no non-artifact swords or armour in 1e or 2e with a bonus greater than +5.  It also perforce limits the size of bonus/penalty ability scores should grant.

When 3e did away with the THAC0 system _*as it existed in D&D*_, it opened up the potential bonuses to infinity and beyond.

This is not a necessary function of order of operation, but it is a strongly implied function of order of operation using the "-10 to 0 to 10" scale that TSR-D&D uses.  It is clear in TSR-D&D that AC 0 is important.  When you've achieved a negative-number AC, you've got a good AC.  

In 3e or 4e, using BAB, there is no "good AC" implied.  Indeed, if "A 30th level Soldier creature has a max of AC 46" it implies that the BAB progression, _*as actually used in D&D*_ tells you nothing about what is inherently good or bad as an AC.  What is a "good" AC becomes a function of level, requiring more calculation related to non-AC factors in order to become useful.

This is true no matter what scale of range is used with THAC0, so long as 0 remains the fulcrum point.  It is, simply put, inherently easier to grasp in terms of game balance, if not in terms of function.  THAC0 _*strongly implies*_ a limited range, whereas BAB strongly implies a greater, and possibly unlimited, range.

One merely has to examine each edition of D&D to see that these implications hold true in the actual design of the game......and in the case of 3e, at least, in the eventual problems inherent in the game system itself.

(And, yes, a game can be designed where BAB doesn't cause these problems, but doing so requires a level of non-intuitive training implicit in the rules that is at least as problematic as that required by THAC0.  I think that this training is worth it, mainly because it falls only on the GM's shoulders rather than the shoulders of everyone at the table, but it would seem foolish to me to ignore that said non-intuitive thinking must be cultivated.)

YMMV, of course.


RC


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## Obryn (Mar 2, 2009)

justanobody said:


> Prove it.
> 
> Using 1st, 2nd, 3rd, and 4th.
> 
> ...



Okay?

BAB + dice roll + modifiers = AC able to hit.

If your system has too many modifiers, this isn't THAC0's or Attack Bonus's fault.

I can, for example, do the following to 2e:

(1) Re-calculate all ACs by calculating 20-OriginalAC, so 10 stays 10, 0 becomes 20, and -10 becomes 30.

(2) Turn THAC0 into an attack bonus by calculating 20-THAC0

(3) Apply all modifiers, such as Strength, magic weapons, etc. to that attack bonus.

During combat, roll a d20, add your attack bonus, and see what AC you hit.

THAC0 is a procedure, pure and simple.

-O


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## Obryn (Mar 2, 2009)

Raven Crowking said:


> This is true for two reasons:
> 
> (1)  In relation to the much argued about human cognition, AC 0 is automatically significant, whether or not the system extends to 100 and -100.  The system, by its very nature, tells you where the "center point" it balances upon is.
> 
> (2)  Related to the above, when you set the worst high AC, the "center point" automatically suggests the best low AC.  Thus, in the system as presented, the worst AC is 10, and the best AC is -10.



I don't know that these naturally follow from one another, even in human cognition.  Knowing that 10 is the worst and lower gets better doesn't give me a reason to believe that there's a "floor" at which it _can't_ get better.

Additionally, setting 10 as the worst is an arbitrary decision.  It's based on factors external to THAC0/BAB.  It could just as easily be a "normal person" difficulty, with other factors increasing it above 10.



> Fair enough.
> 
> OTOH, you should also clarify that your clarification doesn't relate to the THAC0/BAB paradigms in any edition of D&D to date, whereas my point that you are clarifying does.
> 
> RC



I'm talking about the mathematical procedures of THAC0 vs. Attack Bonuses, and which is simpler.  That's pretty much it - the original argument was that THAC0 is quicker and easier, and my posts are written with the OP in mind.

-O


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## justanobody (Mar 2, 2009)

justanobody said:


> Prove it.
> 
> Using 1st, 2nd, 3rd, and 4th.
> 
> Provide each equation with EACH possible modifier to derive a to-hit number for each system.






Obryn said:


> Okay?
> 
> BAB + dice roll + modifiers = AC able to hit.
> 
> ...




*BAB + dice roll + modifiers = AC able to hit.*

You failed to identify EACH possible modifier as was asked for. Would you like to try again? You just lumped it as "modifiers". What are they for, when can you get them, when do you use them, etc?

*(3) Apply all modifiers, such as Strength, magic weapons, etc.*

That does not provide the equation with EACH possible modifier. You provided an incomplete equation.

BAB as a variable means Base Attack Bonus. That s a number you can plug in.

Dice Roll as a variable means another number you can just plug in to the equation from reading the dice.

Modifiers is ?????

What are you plugging in there? is it positive or negative? Where do i find this ONE number called modifiers?

*Provide each equation with EACH possible modifier to derive a to-hit number for each system.*

I expect to see 4 equations total. Each one should contain places for ALL possibile modifiers and including them.

+ weapon bonus
+ weapon penalty
+ strength bonus

for EACH possible modifier in the system for tHAT equation.


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## Umbran (Mar 2, 2009)

justanobody said:


> for EACH possible modifier in the system for tHAT equation.




Um, how about we chill out just a bit.

At the moment, you are arguing rather strongly about something that is not different between the THACO and BAB formulations.   They are mathematically equivalent - so the only issue is where the modifiers enter, not whether or not they are present at all.

I would prefer the tone start leaning away from trying to "win" the argument here.


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## Raven Crowking (Mar 2, 2009)

Obryn said:


> I don't know that these naturally follow from one another, even in human cognition.






> I'm talking about the mathematical procedures of THAC0 vs. Attack Bonuses, and which is simpler.  That's pretty much it - the original argument was that THAC0 is quicker and easier, and my posts are written with the OP in mind.




Of course, it should be noted that the argument that "subtraction is harder (or not easier) than addition" suffers from the problem that "I don't know that these naturally follow from one another, even in human cognition", although I would argue that both, in fact, do.  

In terms of at-the-table mechanics, I don't think THAC0 is difficult, but I agree that BAB is easier.  Likewise, _*provided that the designers supply the tools to do so*_ determining balance from BAB need not be difficult, though I would argue that THAC0 is easier.

Six of one, half a dozen of the other.

(IMHO, of course, positive AC has won out, hence its use in RCFG, so I don't think we disagree overall.)


RC


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## justanobody (Mar 2, 2009)

Umbran said:


> Um, how about we chill out just a bit.
> 
> At the moment, you are arguing rather strongly about something that is not different between the THACO and BAB formulations.   They are mathematically equivalent - so the only issue is where the modifiers enter, not whether or not they are present at all.
> 
> I would prefer the tone start leaning away from trying to "win" the argument here.






Chill out on what, and what tone?

I restated the proof required to quantitatively show what part the modifiers play in all the to-hit systems in order for Obryn to prove that they are not connected and do not add extra layers of complexity to the BAB system.

There is no tone to it. When the equations are presented as asked for, it will be clear on two things:

1- The modifiers and number thereof within a given system ads extra layers of complexity to the to-hit system

2- The BAB system has such a vast amount of possible modifiers that it becomes intrinsically a more complex system than THAC0

Which would prove Obryn in correct in saying the modifiers are separate, and they don't play that large a role in the complexity of the systems. Unless by providing those detailed equations he can prove myself wrong in that the number of possible modifiers from various things are in no way connected to the to-hit systems, and even still they do not add additional complexity to the systems.


All Obryn was asked for was proof that his/her assertion was correct with qualitative evidence.



> The number of modifiers is another completely separate issue. It has absolutely nothing to do with THAC0 vs. Attack Bonus.




I disagree and require proof of that assertion. Without access to 3rd edition books I cannot prove that assertion wrong, but the burden of proof lies with the one making the claim that it is so, such as Obryn did. Therefore I still await the proof of said claim.

Anyone feel free to somehow show that a "number of modifiers is a separate issue", or that it has "nothing to do with THAC0 vs Attack Bonus."

Math has no feelings, no emotions, no tone. This is what I have been saying from the start. If someone wants to read emotions or tone into anything I have written so far, then they are looking for something that is simply not there to begin with.

My previous claims still stands undisputed with proof. THAC0 is efficient and simple.


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## Mercutio01 (Mar 3, 2009)

No, your claim was more efficient and simpler than BAB, which has not been proven.


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## Bullgrit (Mar 3, 2009)

As someone who has a 2nd grader currently dealing with subtraction, I offer this anecdote about teaching the concept:

Total Bullgrit

It ain't as immediately easy as you think.

Bullgrit


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## justanobody (Mar 3, 2009)

Mercutio01 said:


> No, your claim was more efficient and simpler than BAB, which has not been proven.




No and i did not even use simple like i said above but the original claim was:



justanobody said:


> THAC0 works efficiently and easily.
> 
> That is all there is to it.




I said nothing about BAB there.


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## Obryn (Mar 3, 2009)

justanobody said:


> *BAB + dice roll + modifiers = AC able to hit.*
> 
> You failed to identify EACH possible modifier as was asked for. Would you like to try again? You just lumped it as "modifiers". What are they for, when can you get them, when do you use them, etc?
> 
> ...



Could you maybe clarify how you see this as different between THAC0 and BAB?  I'm genuinely confused.

You've listed a THAC0 calculation which doesn't list out modifiers for ability scores, equipment, specialization, situational modifiers, etc.

So, neither did I.

Apart from the situational modifiers (and maybe the "etc."), all of these are figured out ahead of time.  And this is using both attack bonuses and THAC0.  It's not like anyone sits at the table and adds everything back together for every attack, right?

I simply don't see what you're arguing here.

-O


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## Remathilis (Mar 3, 2009)

justanobody said:


> I am just saying 2+2 will not change to 5 just so Jethro is right. Jethro just has to accept that 2+2=4.
> 
> Everyone does not interpret number the same way either. Psychology tells you that people experience everything different from the next person. So the easiest way is the one that is common to all.
> 
> ...




While I am not accusing you of of intellectual snobbery, this strikes me as similar to the arguments some people use to justify the "dumbing down" of every other edition of D&D:

"Gygaxian prose speaks to people who are his equals and have higher level of learning, unlike the dry, lifeless prose of 2e."
"Otis Artwork evokes the feel of classic S&S, not anime kids with buckle-n-spike armor and buster swords."
"At-will Powers? Bah! That's so MMORPG! D&D is a video game now."


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## justanobody (Mar 3, 2009)

I said use mine as a starting point for that set to expound on what the modifiers are.

My equation for players to use with THAC0 will not suffice. It was just a starting poitn for you.

So in place of modifiers, what are those modifiers?

+weapon bonus
+strength bonus
+dexterity bonus
+speed penalty (?)

etc

I just didnt list them all out. You claim they are the same effect, but I think there are quiet a bit more to BAB system of to-hit than with THAC0.

Which while using only addition (except for pentalties) BAB adds a LOT more tot he equation.

As RC said there is near infinite modifiers in the BAB system. Because the system has no limit on AC and to balance this has no limit on the number of modifiers.

Within THAC0 you must fit within a specified range. Once you hit the boundary that is it. Under THAC0 you cannot have a bonus great than 10 to a die roll, and cannot have a penatly greater than 10 either. so your modifier ranges from -10 to 10.

With BAB, you can have penalties into oblivion and the sky is the limit on bonuses....how else would the system allow to hit a AC500 should someone decide to make one?


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## justanobody (Mar 3, 2009)

Remathilis said:


> While I am not accusing you of of intellectual snobbery, this strikes me as similar to the arguments some people use to justify the "dumbing down" of every other edition of D&D:
> 
> "Gygaxian prose speaks to people who are his equals and have higher level of learning, unlike the dry, lifeless prose of 2e."
> "Otis Artwork evokes the feel of classic S&S, not anime kids with buckle-n-spike armor and buster swords."
> "At-will Powers? Bah! That's so MMORPG! D&D is a video game now."




Well you can take it however you want, but if you don't like chasing and hunting a little ball around for over a mile, then you have no reason to complain, just don't play golf and find an activity that suits you better, or get someone else to do part of it for you. Everything is not made for every person to like, nor should it be. That is a part of being an adult, in knowing that you don't have to like everything, and it doesn't have to change just so you will like it.

Call it snobbery if you will, but I call it mature for someone to know that everything wasn't made FOR them specifically, and many things they will not like.


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## Obryn (Mar 3, 2009)

justanobody said:


> I said use mine as a starting point for that set to expound on what the modifiers are.
> 
> My equation for players to use with THAC0 will not suffice. It was just a starting poitn for you.
> 
> ...



Again, these are things *external* to the basic mathematical procedures.

3e has more possible modifiers to attack rolls than 1e does.  This is not, however, inherent to an Attack Bonus system.

Would you agree that it's easy to convert 1e or 2e to an Attack Bonus system?



justanobody said:


> Call it snobbery if you will, but I call it mature for someone to know that everything wasn't made FOR them specifically, and many things they will not like.



...and therefore they shouldn't try to change a game to make it more palatable to them? 

Seriously?

-O


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## Raven Crowking (Mar 3, 2009)

justanobody said:


> As RC said there is near infinite modifiers in the BAB system. Because the system has no limit on AC and to balance this has no limit on the number of modifiers.




This is true in (say) 3e; but note that this does not _*have to be true*_.  

Increasing the number of modifiers with an open-ending system is intuitive because it is a way to make small differences meaningful, and because the pitfalls of doing so are not immediately obvious.

A BAB (or positive AC) system can be designed where this problem does not occur.  There are several retro-clones doing this right now, and at least one retro clone that uses _*both*_ positive and negative AC, so that the end user can choose which one he or she prefers.

What I noted is an inherent pitfall in using positive AC in the design process (including sub-design, such as DMs making houserules, new monsters, etc.), not in the actual at-table use of the system.

To my mind, these are two different issues.  Both relate to how easy it is to use THAC0 or BAB, but they relate to how easy they are to use in two different circumstances.  Game designers who want to use an AC system reminiscent of _*some*_ edition of D&D merely decide whether ease-of-use at the table or ease-of-use in the design process is a better goal.  

As I've said a few times now, I myself chose ease-of-use at the table.

YMMV.


RC


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## Raven Crowking (Mar 3, 2009)

Obryn said:


> ...and therefore they shouldn't try to change a game to make it more palatable to them?
> 
> Seriously?
> 
> -O




Careful, Obryn.  That's my line of reasoning re: 4e!  

RC


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## Obryn (Mar 3, 2009)

Raven Crowking said:


> Careful, Obryn.  That's my line of reasoning re: 4e!
> 
> RC



Eh?  I think it's awesome when people house-rule stuff to make it better for them.

I sometimes caution that the change might not do what they think it will, or note that as a player/DM I might not like it, but house-ruling is a grand old tradition that dates back to the glory days.

-O


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## Raven Crowking (Mar 3, 2009)

Obryn said:


> Eh?  I think it's awesome when people house-rule stuff to make it better for them.
> 
> I sometimes caution that the change might not do what they think it will, or note that as a player/DM I might not like it, but house-ruling is a grand old tradition that dates back to the glory days.
> 
> -O




Maybe not obvious, but I was going for "funny".

That's what passes for humour at Casa Crowking.


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## Obryn (Mar 3, 2009)

Raven Crowking said:


> Maybe not obvious, but I was going for "funny".
> 
> That's what passes for humour at Casa Crowking.



ooops. 

-O


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## Thondor (Mar 3, 2009)

Well the two of you made me laugh. That's pretty awesome.

Probably my biggest issue is the prevalent attitude on these boards that "of course BAB is better", sometimes I find it a little grating.

I'd really love to write a long complicated post in response to all the impressive discussion but . . . I have to go plan some games now!


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## Lanefan (Mar 3, 2009)

I've never had a problem figuring out or explaining that lower AC is better, but I've still never grasped THAC0.  And I think I've figured out why, as something's just occurred to me while reading this that probably should have occurred to me many years ago, but didn't:

The fundamental change from pre-THAC0-using D+D to the same game using THAC0 is that built into THAC0 is your fight level, which players previously did not know (usually) but could now figure out in a heartbeat.  Starting out with a 1st-level MU, a player didn't know she fought like (in effect) a -1th level Fighter; he only knew she was bad at it.  And one's fighting skill got better, in RAW 1e, in odd jumps and starts that once again the players did not know the specifics of.

And with those numbers hidden, a DM could painlessly tweak them.  I did, a long time ago, to smooth out many of those strange jumps...but the numbers are still hidden.  Which is, looking at it now, probably why I never saw the point of THAC0 as a system...as DM I still had to do just as much math as before, *plus* work in the difference between the target's AC and 0.

All I need from my plaeyrs is their roll plus bonuses (at least, those they know about).  I work out the rest; it's pretty easy:

*Player*: "I rolled a 12, plus 2 for weapon and 1 for strength; total 15."
*Me* (unspoken): "OK, the chart says you fight like a 4th; the AC is 2; no oddball stuff going on here, so total is 21."  (spoken) "You hit." (or more descriptive words to the same effect)

Note this gives the same result as using THAC0; this particular character's THAC0 would be 17 - the remaining 4 to get to 21 come from the character's fight level; 21 is still the magic number.

Lanefan


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## Leatherhead (Mar 3, 2009)

I cheated.

I had a handy-dandy table to look up all my THAC0 rolls on. The chart made it even easier to use than doing actual math, and I never had to explain it.


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## Philotomy Jurament (Mar 3, 2009)

Leatherhead said:


> I had a handy-dandy table to look up all my THAC0 rolls on. The chart made it even easier to use than doing actual math, and I never had to explain it.



This is what I do, too.  No calculation involved, fast, and straightforward.  Back in the day, I had a lot of it memorized.  I've forgotten some of that, but as I'm running the old systems, again, it's slowly coming back.

I'm always surprised by the strong feelings on the question of THAC0.


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## Keefe the Thief (Mar 3, 2009)

It comes from experience. Loads of people have played, say, Baldurs Gate or the Gold Box games. And it happens again and again (at least to me) that you explain the basics of the game to a new roleplayer and he looks at you and asks:
"Say. This game. Isnt using that, you know, Thatco thing? Which starts at 20? No? Phew."
The problem here is that deep in-system analysis is not that important. Its first-contact experience that defines ease of use. And to most of my players "you start at +0 and go up" is indeed easier and less intimidating than "you start at 20 and go down, except sometimes its a little more complicated than that. Here, take this chart."


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## Philotomy Jurament (Mar 3, 2009)

The way I approach it, "Armor Class" could just as easily be a letter, rather than a number that is used in a formula.


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## Janx (Mar 3, 2009)

a whole bunch has been said.  I guess I'll say what my experience is.

I got started in 2e, but we mail ordered the books and initially got 1e PH, and 2e DMG.  Figuring out combat was interesting, but it did give me insight into the earlier edition.  (We also did send the 1st PH back, after a few sessions and got the right one).

In early 1E (as I understand it, the Wilderness Survival Guide introduced THAC0), all the combat was resolved by looking up on tables.  If I recall, it was the Armor table that had that data.

THAC0 math comes out the same as the table look-ups.  BAB comes out the same (per same armor bonus, and to-hit bonus).  It's just a different way of expressing it.

For me, THAC0 was better than those tables.  Doing easy math is easier than looking it up on a table.

BAB was better than THAC0, for 2 reasons. Firstly all numbers went UP as they got BETTER.  High was good, Low was bad.  Much easier for new people to get.

Secondly, BAB was better than THAC0, because as a DM, I did not have to disclose extra data to the player, namely the AC, nor did I have to do the THAC0 math for the player so I wouldn't have to disclose the AC.  Whereas, with BAB, the player knows all the data he needs to perform the math (BAB + die roll), he tells me what his total was.  I do the comparison, and tell him if he hit.

Note: I'm not concerned with players figuring out the AC, or anything, just that the initial encounter with a new enemy, the AC should be a secret, and THAC0 gets in the way of that.

Also, I'll note, that the players I find that have trouble, are the same ones who don't precalculate their static values by each weapon.

In 2e or 3e, I ALWAYS took my base number, and applied any strength and weapon bonuses and wrote it down next to each weapon (as it might be different).  I even circled it.  This meant, I already had a good chunk of the math down, and the only extra data I needed at attack time was die roll and situational modifiers (which are rarer).

The "math is complicated" crowd are the same people who are addding up their BAB, the strength, their magic weapon bonus, their specialization bonus for EVERY attack roll.  No matter which system you play, that's going to be moe work.


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## ehren37 (Mar 3, 2009)

Korgoth said:


> I guess I really am a genius. I never found THAC0 confusing in the slightest, even as a child.
> 
> Maybe you guys just don't do subtraction enough. I'm sure you could get better with practice.




I can drive a car with the ignition in the trunk and the gas and brakes on the ceiling. It doesnt mean its a good design.

I'm still astounded people defend 1st edition's  design. Even as children we swapped to something more like 3e. When 10 year olds realize the design flaw of subtracting an armor bonus, you've failed at game mechanics.


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## Philotomy Jurament (Mar 3, 2009)

Janx said:


> In early 1E (as I understand it, the Wilderness Survival Guide introduced THAC0), all the combat was resolved by looking up on tables.



Nope, not the first.  I don't know if it's the first, but the 1e DMG references THAC0 in the appendix that lists all the monsters.  Also, it's not THAC0, exactly, but the original D&D _Monster & Treasure Assortments_ list an "AL" or attack level which is the monster's "base number to score a hit on an unarmed opponent (armor class 9)."



> THAC0 math comes out the same as the table look-ups.  BAB comes out the same (per same armor bonus, and to-hit bonus).  It's just a different way of expressing it.



Yeah, that's my view.  I didn't see THAC0 as a great innovation, and I don't see BAB as a great innovation, either.  To me, the difference is like saying rolling a d20 and aiming for 11 or higher is better than rolling a d6 and aiming for 1-3.  I get the point that using a d20 and aiming for high rolls makes the roll more like other types of rolls used in the game, but I just can't muster up any admiration for that.  It's just not a significant change, to me (no "oh wow, this is so much better").  I just shrug: "hey man, if it works for you, it's cool."


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## Philotomy Jurament (Mar 3, 2009)

ehren37 said:


> I'm still astounded people defend 1st edition's  design. Even as children we swapped to something more like 3e. When 10 year olds realize the design flaw of subtracting an armor bonus, you've failed at game mechanics.



Damn, I wish I had the intelligence of a 10 year old and could appreciate the clear superiority of BAB (and recognize 1e's f'd-up design).  Perhaps if I stick around and keep reading, I'll realize how flawed my perception is and elevate my mind.


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## Reynard (Mar 3, 2009)

ehren37 said:


> I can drive a car with the ignition in the trunk and the gas and brakes on the ceiling. It doesnt mean its a good design.
> 
> I'm still astounded people defend 1st edition's  design. Even as children we swapped to something more like 3e. When 10 year olds realize the design flaw of subtracting an armor bonus, you've failed at game mechanics.




I doubt your credentials to evaluate "good" game design, based primarily on this post.


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## Umbran (Mar 3, 2009)

Folks, things are getting way too personal in here.  The cracks about intelligence, especially.  

Everyone is hereby warned to treat each other with utmost respect.  In general, deal with the position, not the person speaking.


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## Thondor (Mar 3, 2009)

Thanks for the moderation Umbran, I think we can all use the reminder to be more curtious and assume other posters intentions were benign.

*Surprising Variety*

One of the possible advantages of THAC0 (and one that this thread has let me discover) is that there is a surprising amount of ways for a group to approach it, to use it in game.

It is easy to use (or make) a _chart_ with THAC0 so if your more comfortable with that you can. (Both a chart for the DM or for the players.)

_Players don't know anything_.
 If you want a game were the players don't know their THAC0, or how good a particular magic item is, this is how 1e is designed. Their also less likely to bother figuring out opponents AC. Here THAC0 works well, just note the players THAC0 any of its variations due to modifiers and the DM makes the calculations or uses a chart.

_Players know their THAC0 but don't know AC, and don't do math_. 
Player states the roll and their THAC0 (leaving rare situational modifiers to the DM, or not as the group has decided) DM calculates THAC0 - AC

_Players know their THAC0 but don't know AC, and use chart.
_Player rolls, checks their THAC0 table and reports what AC they hit. DM compares to AC

_Players know their THAC0 but don't know AC, and do math_,
Player rolls, calculates THAC0 - roll, then state the AC they hit. DM compares this to opponents AC 

_Players know their THAC0 and know AC._
The player can actually do the calculation any way they want, though I maintain that THAC0 - AC would be easiest (this determines how high the roll needs to be), at which point they tell the DM if they hit.

_If you prefer addition_
You can add roll + AC to find if your THAC0 is high enough to hit. (The DM could do that of course, I don't like that approach because then you do the calculation each round).


While any of these approaches could be used with BAB, I think the Attack Bonus system really encourages only one approach.
Both systems can lead to confusion at the Table. In my experience, because I can pick how THAC0 is used at my table, it has lead to less.


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## Thondor (Mar 13, 2009)

Apparently everyone agrees with me now .


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## Obryn (Mar 13, 2009)

Thondor said:


> Apparently everyone agrees with me now .



Nope, just bored with the topic.

-O


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## TwinBahamut (Mar 13, 2009)

It is probably a little late for all of this, but I may as well weigh in my opinion.

My experience with THAC0 is a little unique, simply because I had to actually learn the system because I played in 2E adventures (actually, I DMed them for my brother, with no "experienced player" to tell us how to do things), but I never really immersed myself in those rules for any period of time. It was just me and my brother, having to figure out how the entire system works using a "D&D Adventure Set" with a few adventures and pre-made characters. Shortly afterwards, we acquired real D&D books, which ended up being the first-printed 3E core books. And my _first_ reaction to reading a core rules book for the first time was that the BAB system was a tremendous improvement over THAC0. I didn't even realize that the difference was a result of an edition change, I just liked that it was much easier to use.

THAC0 is really something that you need to immerse yourself in to really "get". With all of these arguments in this thread, there is one question that I have not seen be brought up, which is actually part of my biggest complaint about THAC0. Why, exactly, is the entire thing phrased as your ability to hit AC 0? What is so special about AC 0? When I was actually using the system, I had the hardest time even really grasping what in-character quality THAC0 was even really supposed to represent. The fact that is explicitly references game terminology like numbered AC and dice rolls, rather that character qualities, made it worse.

I mean, it is more than just a difference between adding or subtracting. A "To Hit AC 20" system would possibly be just as confusing as a THAC0 system, even if it used nothing but positive AC values and positive attack modifiers. The problem is the mental task of converting the "To hit AC X" number to the number you need to roll in order to hit an _actual_ AC. It feels like the completely wrong approach, since it feels like someone did work for you, but it was the wrong work, so every actual task involves undoing a step and then redoing it properly.


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## Thondor (Mar 14, 2009)

There were some people who addressed why THAC0 uses the target number of Zero. 

It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)

Hmmm, I'll have more to comment later.


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## TwinBahamut (Mar 14, 2009)

Thondor said:


> There were some people who addressed why THAC0 uses the target number of Zero.
> 
> It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)
> 
> Hmmm, I'll have more to comment later.



That misses the entire point. The problem isn't the exact target number, the problem is that the entire system is _based_ around a target number. It is a system in which the math of your basic combat ability is implicit, rather than explicit. It is a system that only works intuitively if you are targeting a foe with AC 0.

Let me phrase this a different way.

In the attack bonus system, the different numbers involves all have direct connections to understandable qualities. Basically, if "luck" (die roll) + "skill" (attack bonus) >= "the enemy's ability to defend itself" (AC), then the hit connects. It is easily intuitive. However, in the THAC0 system, it is closer to "your ability to hit a moderately tough enemy" (THAC0) - "the defense of your current enemy" (AC) = "how lucky you need to be" (target die roll). It is mathematically the same, but it is far more removed from easily understood physical concepts, and thus is harder to use and is less easily remembered.

I'm not sure if I am arguing this perfectly, but there is a conceptual difference that makes the attack bonus system much more intuitive than the THAC0 system. I mean, I am no idiot at math (I am willing to bet that I am well above the average for these boards in terms of mathematical skill), but it took me several hours of practice to understand THAC0 originally (and I still can't remember what you are supposed to subtract from what), but I was able to grasp the attack bonus system instantly.


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## Remathilis (Mar 14, 2009)

Thondor said:


> There were some people who addressed why THAC0 uses the target number of Zero.
> 
> It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)
> 
> Hmmm, I'll have more to comment later.




So would the system have worked any better/worse with Thac10? (the worst AC)

A 1st level PC (any class) has a thac10 of 10 (must roll a 10 or better on a d20). Each point he rolls higher is a lower AC (11 = 9, - 20 = 0). If he begins to break higher than a 20, he gets negative AC (21 = -1).

Each time he levels (assuming a fighter-type) his thac10 lowers one point. 

Mathmatically, it would be the same but you wouldn't have to subtract positive ACs, as you would "starting in the middle"?


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## HardcoreDandDGirl (Mar 14, 2009)

First I have to say at 8 years old (First time playing) I got thac0, by age 10 I could explain it, and figure it without charts or books. And as much as I never failed math, it was far from my best subject in school




Remathilis said:


> So would the system have worked any better/worse with Thac10? (the worst AC)
> 
> A 1st level PC (any class) has a thac10 of 10 (must roll a 10 or better on a d20). Each point he rolls higher is a lower AC (11 = 9, - 20 = 0). If he begins to break higher than a 20, he gets negative AC (21 = -1).
> 
> ...





Back a few years ago I herd a rumor that TSR had worked on a 3e of there own, like the editions before mostly making optional and common house rules into the book. One thing I herd was that it was Thac10 instead of Thac0. 

This same rumor also said that they didn’t have the resources to finish it, and when WotC bought them out, they scraped 85-90% of the work and started almost from scratch on there 3e.

I sometime wonder what that system would have looked like. Your example here now gives me some idea.

does anyone rembere the Mthac0???


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## Thondor (Mar 14, 2009)

Remathilis said:


> So would the system have worked any better/worse with Thac10? (the worst AC)




Well . . . I don't think so.

Something that I think hasn't been addressed so far is that by using the THAC0 system, you deal with fewer large numbers in your math. Which can be nice.

Yes oK THAC0 itself can be a high number, however AC rarely goes above 7 or below -7. 

Lets take an example of a 14th level fighter in both systems. No magic weapons, str bonus, or other benefits for simplicity.

Figther has a THAC0 of 6. The DM decides to tell the fighter that his opponent (a Pit Fiend) has a AC of -3.
The player does the math 6 - -3 = 9. He rolls twice for his two attacks. Both are 9 or better! That's two hits!

Fighter has a BAB of +14/+9/+4 . The DM decides to tell the player the opponent (a Hezrou) has a AC of 23. 
The player rolls a 6. 6+14 = 20, compares it to the AC not good enough. 
The player rolls a 18. He doesn't even bother to do the math, he knows he hits.
the player rolls a 7. 7+4=11 is nowhere near enough.

Sigh, the default presumption in both systems that the DM keeps the AC hidden makes them harder to compare. (default is player does math in BAB and DM does math in THAC0)

I suppose my point is I find it easier to take a Large Static # - A small # <= a Variable #   (ThAC0 - AC<= roll) then to take a
 Variable # + # or # <= Large static # (roll + 1st BAB or 2nd BAB <= AC)

Aside: really find it difficult to communicate math on the forums.


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## Moleculo (Mar 14, 2009)

Thondor said:


> Well . . . I don't think so.
> 
> Something that I think hasn't been addressed so far is that by using the THAC0 system, you deal with fewer large numbers in your math. Which can be nice.
> 
> ...




Hehe the large numbers argument's a little weak considering that you bring up subtracting negative numbers in your example .

Anyway, I think the beauty of BAB is that it follows the unified D20 mechanic, which is an importance that can't be overlooked. THAC0 was one of the dozens of separate mechanics that the players and DM had to memorize to resolve anything in 2nd Ed. 

Even if we were to suppose that THAC0 and BAB were equal, the benefit of having a rule that is internally consistent with the rules as a whole would give the win to BAB. The standardization not only made the combat system make sense, but it contributes to people picking up the game more quickly.  I mean why were swords "+1" in 2nd ed? Why weren't they "-1"? They certainly didn't increase your THAC0. Oh so anything that gives me a "plus" to hit, actually decreases my THAC0? Huh?  

Secondly, the shift in math can't be ignored. The DM is running the game. In 2nd ed, he had to keep track of the monster's AC, the players THAC0, and the roll the character made. God forbid the characters do anything that affects their bonuses to hit (such as change to their silvered, non-magical sword...) 

With BAB the DM just needs to know whether the modified roll is greater than or equal to the AC of the monster.  The more work the DM can farm out to the PCs the better. This means the DM can focus on more interesting things that doing math in his head every round.


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## Jack Colby (Mar 14, 2009)

Agamon said:


> Personally, having played both ways for a number of years, I disagree, for two reasons:
> 
> 1. Adding is inherently easier than subtracting.
> 
> 2. Spreading the math from the one DM, who already does way more mental work than the players during the game, to the many players, is easier over the game night.




This.  But I wouldn't discredit anyone for preferring THAC0 or feeling it's easier for them.  For me, THAC0 is more effort to use, and I have never gotten used to it or liked it.  I'll admit there are certain benefits to using it, but I don't mind trading those for easier (for me) calculations and faster, more confident combat actions.


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## Jack Colby (Mar 14, 2009)

Moleculo said:


> Anyway, I think the beauty of BAB is that it follows the unified D20 mechanic, which is an importance that can't be overlooked. THAC0 was one of the dozens of separate mechanics that the players and DM had to memorize to resolve anything in 2nd Ed.




First, memorizing all of those things wasn't necessarily that hard.  I managed to do it, and I'm not that bright!   Second, the many different subsystems also had at least one advantage over the unified mechanic: it meant they weren't as interwoven mechanically, and a bonus here didn't always affect a score there.  In the long run that's a lot less calculating and fiddly bits to worry about during character creation as well as play.  They were also more modular, thus, you could houserule/remove, for example, the saving throw system, without it affecting the entire fabric of the game.

Just some thoughts, and I think it reinforces the OPs idea of questioning things that are "obviously" true.  There are always going to be people who have another view, and if you listen you might not change your mind, but you will probably learn something.


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## Thondor (Mar 20, 2009)

Moleculo said:


> Hehe the large numbers argument's a little weak considering that you bring up subtracting negative numbers in your example .




First the idea that subtracting a negative number is really difficult is strange. I mean that is like grade four math. All a person needs to realize is that it is actually addition.  

The major difference is the number of calculations necessary with BAB.This is especially true for high level:
Usually every single attack, including iteratives require a calculation.
Instead of dealing with 12(roll) + 17(Attack Bonus) every round, plus the iterative attack calculations 
You deal with 4(THAC0) - -4 (AC) once. (which is just 4+4) Until your opponent(s) is dropped. 
             (And yes AC of more then 29 aren't that uncommon in 3rd edition)



Moleculo said:


> With BAB the DM just needs to know whether the modified roll is greater than or equal to the AC of the monster. The more work the DM can farm out to the PCs the better. This means the DM can focus on more interesting things that doing math in his head every round.




At least with THAC0 the DM is really given the option of how he wants to run his game. (and so are the players actually)
1. The players can not know their THAC0
2. The players can know their THAC0 but the DM does the calculations
3. The players do the calculations (they either are told the AC's or calculate what AC they hit).

With BAB your sort of stapled into a one way to do things. Personally I find it quick to either tell the players the AC, or if I want to keep it 'secret' do the calculation myself. In fact its often faster if I just do them myself.


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## Thondor (Mar 20, 2009)

Jack Colby said:


> First, memorizing all of those things wasn't necessarily that hard.  I managed to do it, and I'm not that bright!   Second, the many different subsystems also had at least one advantage over the unified mechanic: it meant they weren't as interwoven mechanically, and a bonus here didn't always affect a score there.  In the long run that's a lot less calculating and fiddly bits to worry about during character creation as well as play.  They were also more modular, thus, you could houserule/remove, for example, the saving throw system, without it affecting the entire fabric of the game.
> 
> Just some thoughts, and I think it reinforces the OPs idea of questioning things that are "obviously" true.  There are always going to be people who have another view, and if you listen you might not change your mind, but you will probably learn something.




Very well said. There are almost always some advantages to doing things a different way. How the collection of advantages and disavantages compare between options is how you should decide. I think most people don't know or haven't fully considered some of the advantages of THAC0 compared to BAB. It certainly isn't naturally inferior.

As an aside the modularity of pre 3.0 A/D&D is one of its great strengths. I personally love the iniative/surprise rule that use a single roll of a d6 to determine if the group is surprised and which group goes first in one roll of a d6. 
Some people don't they replace it with some other mechanism. No worries, it really doesn't effect much else.


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