Why THAC0 Rocks

[Keefe the Thief]

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.

 

[FireLance]

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?

 

[S'mon]

Sorry if this is a little off topic





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.

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.

 

[S'mon]

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.

 

[Beginning of the End]

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.

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?

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?

 

[Korgoth]

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.

 

[wedgeski]

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.

 

[Nymrohd]

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

 

[S'mon]

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.

 

[Nikosandros]

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.