After years of frustrating scope mounting. I never seemed to get the crosshairs plumb. Someone suggested a Wheeler Engineering level. Actually it's two. Works slick. Being an engineer I just put it on and damned if my X hairs were out. Soooo, basic engineering101: read the instructions. Tough to find a level spot on my Ruger MkII so I removed the bolt and used the small flat across the safety. Try it, you'll wonder why you didn't use something like it before.