Improved Armor Focus (Combat)Source Armor Master's Handbook pg. 16
Your mastery makes the most of your armor.
Prerequisites: Armor Focus, base attack bonus +6, proficiency with selected armor.
Benefit: 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.Source Armor Master's Handbook pg. 20 (Amazon)
You can spend 5 stamina points to negate your armor’s armor check penalty for 1 skill check. (See page 16.)