After some trial and lots of error, am I right that you have to back off the top elevation adjusting screw a little, tighten the big thumb screw and finally tighten the top elevation screw? The reason for the question is that if both elevation adjusting screws are left tight, the thumb screw tightening against the elevation screws pinch can cause big variances in windage. This is important to me because it is expensive to zero a Mosin Nagant if you have to do it more than once.