This question relates to how the designers of 3rd edition might have come up with the roll-over Ability Check mechanics from the roll-under Ability Check mechanics of 2e. The problem I'm trying to solve is importing Ability Check mechanics from 3e to 2e. I thought by analyzing the transition from 2e to 3e, I might have a better understanding.
It's pretty common knowledge that you can reverse engineer to-hit rolls in 2e to be similar to those of 3e by:
Base Attack Bonus (3e) = 20 - THAC0 (2e)
AC (3e) = 20 - AC (2e)
But I'm at a loss as to how they might have determined the modifiers for Attributes to go from a roll-under 2e Ability Check to a roll-and-add 3e Ability Check.
I am lead to believe by various forum posts that, when 3e came out, "a lot of people were doing it that way already". If this is true, what were they basing these Ability Check rules on? Supposedly, there might have been articles in Dragon Magazine that included roll-and-add mechanics for Ability Checks. An issue number would be greatly appreciated if someone could provide one.