I am fairly new to the shooting sports and am considering putting a scope or possibly an Aimpoint on my Ruger MK2 (KMK678GC). I picked up one of Clark Customs excellent Weaver scope bases to replace the Ruger propriatory one, and on researching optic devices the term MOA is referenced but I have yet to find an explanation on what it means. It seems critical, as the various scopes use this for quality comparisons.