I clamp the rifle into a sturdy tripod, get it level using a bubble level on the scope base, then mount the scope level with the rifle. I then align the reticle with a plumb line or the horizon and mount/adjust the anti-cant device. I use stabila and starrett pocket levels (mainly because they are multi-purpose and reliable), but the wheeler levels work fine too. Once the scope is in the mount, I usually leave it in there, even if I move the scope to a different rifle.