THAC0 & AC

[Radagast]

Could someone please explain this to me. I was under the impression that the attack roll plays out as follows. THAC0 of attacker minus the AC of attackee. The attacker must then roll that number or higher on a 20 sided die to inflict damage. That makes sense. But what about when the AC goes below zero? Then you wind up adding the two number instead of subtracting. Does this make sense? If so, how?

[Morgan_Corbesant]

if you factor in strength bonuses, weapon bonuses, specialty bonuses, elves have a +1 to hit with long, short swords, and all bows as well. factor all of this in, and it is indeed possible to hit an AC below zero.



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Morgan Corbesant, Elven BladeSinger, Captain of the army of the Seldarine

Okay, when D&D first came out, they used a 20 sided die. Now this is still used internally in the game BG. Say you have a THAC0 of 15, that means that you need to roll a 15 on that 20 sided die to hit AC 0. Say you're THAC0 was 10, then you'd only need a 10 to hit AC 0. If you're THAC0 was 12 and your enemies' AC was 4, you would need to roll an 8 on that 20 sided die. Understand?

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Formidable Flirty Fishy Sorcerer of the HADB

[Radagast]

Ya. I got that part. I wrote it in my message. Now let me give you my example:

1) If my THAC0 is 7 and your AC is 3 then I have to roll a 4 or higher on a 20 sided die to do damage. (From the formula THAC0-AC= what I must roll to do damage.)
2) If my THAC0 is 2 and your AC is -1 now I have to roll a 3 or higher to do damage. (From the formula THAC0-AC= what I must roll to do damage.)

That's crazy! You have a BETTER AC yet it is EASIER to do you damage. That is because of the lower THAC0. I think I have just figured out that THAC0 is easily just as important as AC. A revelation to me although probably not to many of you.

[Dafo5]

no if you had a thaco 0f 19 and you trying to injure a -1 then youd need to roll a 20 i have a character with -11 but they still can be hit as a roll of 20 is always a hit and likewise a roll of a 1 is always a fail meaning you cant be invincible (without cheating of course) itd be a bit too easy if you could dont you think. i know what you mean though cos i found it strange at first!

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"The day shall come when you will finally know and understand me, but untill that day you will live only a myth. Never forget that for you must always wait in fear!"

[SixOfSpades]

Baldur's Gate uses the AD&D 2nd Edition rules, which I agree can be quite confusing in the matter of AC and THAC0. The 3rd edition changes those number systems around, so that the higher the number, the better it is. MUCH less confusing that way.

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Boots of Stealth: 1125 gp
Shadow Armor: 7875 gp
Slipping an Oil of Firey Burning down the back of Sarevok's armor: Priceless

[Radagast]

Six,
Which number do they change around in the 3rd? I would assume AC stays the same (the lower the better) so you must mean THAC0. But that doesn't make sense either. Now if my THAC0 is 15 and I am trying to hit someone with an AC of 5 then I must roll a 10. But if my THAC0 is 17 (which you say is the better THAC0 in 3rd edition) and I am attacking a guy with an AC of 5, now I have to roll a 12 or higher. That definitely doesn't make sense. My THAC0 got better and his AC stayed the same yet it is harder to hit him.
I AM SO LOST WITH THIS. I NEED A MATHEMATICIAN.

[SixOfSpades]

Don't worry too much about it, Radagast. Just remember that in AD&D 2nd Edition, and Baldur's Gate, the formula is, as you said, THAC0-AC=what you need to roll to score a hit. THAC0 is actually even MORE important than AC, because you should try to be attacking the enemy more often than you're being attacked.

I'm told that in the 3rd Edition rules, BOTH numbers were changed around; a positive AC is good, and a positive THAC0 is good. Don't ask me for any formulas, though.

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Boots of Stealth: 1125 gp
Shadow Armor: 7875 gp
Slipping an Oil of Firey Burning down the back of Sarevok's armor: Priceless

[Chris77Se]

In the 3rd Edition the system has been totally changed. Yo now get an attack modifier or bonus (depends on class and stats), which you add to the roll of one d20. If this value is higher than the AC of your opponent, you hit him.