Geas

I realize with Elbow and Knee, a lot of the damage is determined by the armour ratings of one's arms and of one's legs. My question is, particularly with elbow, does it check both arms, or one arm over the other? Does one elbow with one's main arm or with one's off arm? If someone could enlighten me on this, I'd appreciate it.

Only the armor on one leg or arm is checked. If there two possible location one is choose randomly.