All window manufacturers hand their product as viewed from exterior. If hinge is on left from exterior: left hand window unit. If hinge is on right from exterior: right hand window unit. An easy way to hand windows from the inside (where we are most of the time) is to look at what side the lock is on for the window that needs the new operator. If the lock is on the left from the inside then the hinge is on the left from exterior and it is a left hand window unit. If lock is on the right from inside then the hinge is on the right from the exterior and it is a right hand window unit.