You’ll want to level from the base of the mount, ideally on a flat surface that isn’t affected by the built-in 20MOA slope. The best method is to place a small level on the rail section of the mount (if possible) or on the receiver itself to ensure your rifle is level first. Then, when mounting the scope, focus on leveling the reticle rather than relying on the mount’s upper surfaces. A plumb bob or a known vertical reference can help with this. Hope that helps! mybalancenow