Editing Advanced Dungeons & Dragons (section)

===THAC0===
2E took the combat matrices and made them uniform in function. Every class or kit in the game falls under one of 4 categories, and each category has a different rate of improvement. Fighters, obviously, get the best rate, while non-physical fighters get the worst. The statistic used to implement these categories was called THAC0.

'''THAC0''' stands for '''T'''o '''H'''it '''A'''rmor '''C'''lass '''0''' (zero); it's the minimum number you needed to roll on a d20 in order to hit something with AC 0 (which means the lower your THAC0, the better for you). To handle other armor classes, you subtracted the target's AC from your character's THAC0, and then tried to roll at least this number. DMs often did not share the enemy's AC, in which case you would roll a d20, and <s>subtract it from your THAC0 to show the lowest AC that you could hit.</s> wait for the DM to tell you if you hit since it's his job.

Opinions of this mechanic are divided; some say it's overly complicated and non-intuitive ([https://www.penny-arcade.com/comic/2022/04/08/less-is-more-2 negative ACs being a common argument]), while others don't mind all the basic subtraction (also, thac0 progression can just be thought of as to-hit bonus, negating any math besides being able to reverse your added result in order to know what AC you hit). Others just say that no matter how retarded it is, it's preferable to rolling on a table for every attack.