Why THAC0 Rocks

Thondor

Explorer
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.
 
Last edited:

log in or register to remove this ad

Chaos Disciple

Explorer
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.
 

Agamon

Adventurer
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.
 

S'mon

Legend
"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.
 

BryonD

Hero
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
 
Last edited:

Lanefan

Victoria Rules
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
 

Thondor

Explorer
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.

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

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.
 
Last edited:

Umbran

Mod Squad
Staff member
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.
 

Thondor

Explorer
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.
 


El Mahdi

Muad'Dib of the Anauroch
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.:p;) To me, the BAB path seems to be a little less rocky.:heh:)
 

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...
 

Thondor

Explorer
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.
 

BryonD

Hero
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
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.
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.
 
Last edited:

Thondor

Explorer
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...


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.
 

Thondor

Explorer
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.

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.
 

Thondor

Explorer
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.
 

Freakohollik

First Post
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.
 

Remathilis

Legend
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.

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.

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.
 

Ariosto

First Post
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.
 

Level Up!

An Advertisement

Advertisement4

Top