How to set up your shooting glasses for rifle shooting
From Shooting.Wiki EN
Not all of us have perfect visual acuity. So some need glasses while shooting. It's very important to set up the glasses correctly, because otherwise you can make everything right but your shots are everywhere but in the ten. If you're shooting 3 positions the glasses have to be checked in each position, as the position of the head is a bit different.
The center of the lens should be in the middle of the diopter disc. That way the shooter can aim correctly through the lens.
Neither the frame should touch the rifle/diopter nor the lens should touch the nose. Otherwise the dispersion pattern changes from shot to shot.
It's hard for the shooter to set up the frame and lens on his own. A second person should at least check the correct set up of the frame and lens.