Increases AC
Adds +4 to Constitution (thus adding +2 to Fortitude saving throws and +2 to max HP per character level) and +3 to Dexterity (thus, depending on prior Dexterity score, either +1/+2 To Hit with ranged attacks, either +1/+2 to AC, and either +1/+2 to Reflex saving throws).
Adds +1 to AC when used with a 2-handed Ranged weapon. It may not be used with any melee weapon nor with a 1-handed Ranged weapon. Its polished surface also functions as a mirror.