Neither scope rail nor turret top directly correspond to either crosshair, or elevation adjustment.
If you use bipods in the field(you really should) get the swivel models.
Mount one of these to the scope: Scoplevel Anti Cant Leveling Device
Of all the fancy levels out there, only this one can be seen straight on, by the shooting eye, from your aiming position.
Using a gun hold that is comfortable and consistent for you(this will not likely be as mounted in a vise), rotate your scope in loose rings until the top of the elevation turret is spirit level(only a baseline).
-Now, if you use your reticle for hold-offs, you can use any downrange plumb method mentioned, finely rotate scope for crosshair plumb, tighten rings, turn the ScopLevel to plumb & tighten it. You're done.
-If you dial your elevation, you might not be done, but at another baseline.
Shoot a ~40moa plumb line while using your ScopLevel and verify shooting/adjustment is plumb Up & down. If not, you can rotate the ScopLevel that tiny amount to shoot a plumb line. This time you're done.
Now the ScopLevel, mounted to your scope, is your standard.
You can move the scope from gun to safe to gun & back, flip up the ScopLevel, shoulder, rotate scope to spirit level, tighten scope rings, find/set your zero.
That easy from now on -with that scope, having it's ScopLevel previously set.