Wow, that was probably the best explanation you can get on the web - so simple yet so informative (even the dumbest would understand), good work, Witness.
But one thing i find illogic: if armor rating is 10, why the penetr. value of 7 would make an attack do -70%? Does that mean the penetration of 9 would make it -90%, or -50%?
Shouldn't 7 againt 10 be -30%, as 8 against 10: -20%, 9 against 10: -10% and 10 against 10: 0% bonus damage (normal weapon damage)?