Dan I have used the same procedure but at 300 yards. Level gun on bench and crosshairs on line drawn vertical with the level. I like to then set up a paper with the plumb line as far down range as I can and Put a target dot at bottom of line and shoot a group. Dial scope up as many minutes as possible to stay on paper and shoot another group holding on the same target dot at bottom of line. See if group goes left or right. If so the scope is not tracking straight up and needs to be adjusted in rings again. Hope this makes sense!