Your mastery makes the most of your armor.
Benefit(s): The armor check penalty of the selected armor decreases by 1 (to a minimum of 0). You also use your character level in place of your base attack bonus for the purpose of armor mastery feat prerequisites.
Special: You can gain this feat multiple times. Its effects do not stack. Each time you take the feat, it applies to a new type of armor.
Pathfinder Player Companion: Armor Master’s Handbook © 2016, Paizo Inc.; Authors: Alexander Augunas, Robert Brookes, Anthony Li, Luis Loza, and David Schwartz.