RE: Checking Crosshair to Turret Squarness
Okay are we talking square with turrets or in line with the bore? If its with turrets I don't see it. It should be in line with the bore unless all you ever use is the center of the crosshairs. If thats the case then it won't matter if the axis runs 230 to 830 diagonally.
But if you ever hold over or hold for windage then things need to be true to the bore to have any true and accurate relevance. And you need to pay attention to how you hold your rifle such that things are relevant.
Now IF you do hold cant, it better be repeatable. And FWIW if you hold a cant and adjust the crosshairs for said cant, you'll pay in the end. Because your can in standing, sitting, kneeling, prone and other field positions will vary. So if you start true vertical horizontal to the bore in the first place you'll have a solid reference to work with.