A better THAC0?

vivsavage said:

Why not simply use the defender's AC as a modifier to the dice roll itself? No need to recalculate your THAC0 that way, and you don't use any inverse values, so to speak. Mathematically it's the same result, but sees to me to be more intuitive.

If the DM doesn't want to reveal the enemy's AC, the player can simply roll the dice and compare it to his THAC0, giving a number indicating what AC has been hit. For example, if the player with the 15 THAC0 rolls a 17, he announces he has hit AC 2 or better.

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Nagol said:

The DMG mention is disingenuous. The 1e DMG has tables cross-referencing class levels (or hit dice for monsters) with target AC.

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vivsavage said:

To make an attack in 2e AD&D, you subtract the enemy's AC from your THAC0 score before rolling. So if your THAC0 is 15 and the enemy's AC is -1, you subtract -1 from 15, meaning you need a 16+ to hit. While it works fine, many people find the system unintuitive since you are really adding the inverse of the AC to your THAC0.

Why not simply use the defender's AC as a modifier to the dice roll itself? No need to recalculate your THAC0 that way, and you don't use any inverse values, so to speak. Mathematically it's the same result, but sees to me to be more intuitive. If the DM doesn't want to reveal the enemy's AC, the player can simply roll the dice and compare it to his THAC0, giving a number indicating what AC has been hit. For example, if the player with the 15 THAC0 rolls a 17, he announces he has hit AC 2 or better.

Yes? No? Maybe?

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Libramarian said:

To me THAC0 is a must when running AD&D. I consider it a serious aesthetic mistake to convert to BAB. THAC0 is of a piece with the saving throw numbers on the character sheet: if you roll over these numbers, good things happen.

The best way to use THAC0 is to say the attack is a hit if the roll is equal to or greater than the attacker's THAC0, or less than or equal to the defender's AC.

The attacking player compares the dice roll to their THAC0, and the defending player compares the roll to their AC. In most cases this involves no arithmetic whatsoever, making it the most human-friendly attack algorithm of all.

e.g. PC with THAC0 18 attacks monster with AC 7. Roll is 19.
Player: Hit!

e.g. PC with THAC0 15 attacks monster with AC 5. Roll is 4.
DM: Hit!

Positive attack mods are handled by the attacking player, and negative attack mods are handled by the defending player. Negative mods boost the defender's effective AC. A negative AC applies as a negative modifier to the attack roll.

e.g. PC with THAC0 12 attacks AC 3 with +1 from Bless but -4 due to weapon vs. AC adjustment. AC 3 becomes an effective AC of -1. Roll is 11.
Player: Hit, just barely!
DM: Hold on, I have an effective AC of -1.
Player: Darn, I miss!

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