Why THAC0 Rocks

[avin]

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

 

[kitsune9]

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.

 

[Puggins]

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.

 

[Fifth Element]

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.

 

[Dragonhelm]

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'.

 

[Storminator]

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

 

[justanobody]

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.

 

[billd91]

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.

 

[Mallus]

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).

 

[billd91]

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.