Can someone explain armour/damage for me please? :)

[Evalissa]

I played EQ a long time ago, but recently returned and brought a friend with me who never did.
I have forgotten a lot, but likely never had a clue how it worked back then either since I never used to care much for that sort of thing, but now we both do. So, what value is +3 armour to a paladin that has 300?
How would you work out your basic/average dps to compare items? (Damage/Speed is what I have been using but people say there is more to it than that) Thanks [You must be logged in to view images. Log in or Register.]