Armor Penatration

[um104]

What exactly does Armor Penatration do? I know I'm supposed to be the "Air Elementalist Extrordinare", but i still dont get if the 15% AP means that 15% of ur damage goes directly through or 15% of your damage is added again. I've had experiences backing both of these up, like this. Me and my friend, back in beta, each made a guild to go GvG against eachother and test out skills. My Air attack said it did 54 damage, and he calculated his Armor thingy... wuts it called... well, it was 60, so he said it would do 30-something damage w/o the AP. i did the attack, and it did round 47. we tried this again, and it did exactly 59. soo.... help out here?
Air Elementalist Extrordinare... I hope
--um104

[Xircon]

What exactly does Armor Penatration do? I know I'm supposed to be the "Air Elementalist Extrordinare", but i still dont get if the 15% AP means that 15% of ur damage goes directly through or 15% of your damage is added again. I've had experiences backing both of these up, like this. Me and my friend, back in beta, each made a guild to go GvG against eachother and test out skills. My Air attack said it did 54 damage, and he calculated his Armor thingy... wuts it called... well, it was 60, so he said it would do 30-something damage w/o the AP. i did the attack, and it did round 47. we tried this again, and it did exactly 59. soo.... help out here?
Air Elementalist Extrordinare... I hope
--um104

Armor penetration ignores targets armor. If it says 20%, 20% of the attack did full damage and 80% did damage based on the armor defense.