Talk:Armor Penetration/@comment-217.87.153.250-20100928085906/@comment-3067750-20101010162253

Already answered in Armor / Magic Resitance pages.

In X / ( 100 + | X | ) so if you had -100 Armor, by whatever means, the formula would be -100 / ( 100 + 100 ) since +100 is the absolute value of -100, because of this the damage reduction is -50%. Or, if you prefer, it is a 50% Damage increase