You can get rid of THAC0 if you just use this simple rule: roll d20, add the opponent's armor class (plus your own to-hit bonus if any), and a result of 20 or b

You can get rid of THAC0 if you just use this simple rule: roll d20, add the opponent's armor class (plus your own to-hit bonus if any), and a result of 20 or better is a hit.