I have mounted many scopes in my lifetime and have used various methods to level my scope's crosshairs. I have found that the best method is to hang a string with a heavy object and use that as vertical. This method is far from perfect but has always satisfied me since I just click in the elevation. Now I have a NPR2 and I use the vertical crosshair for elevation instead of clicking in. I cannot imagine the amount of error that can be introduced if the crosshair is not exactly vertical. I'd like to hear from those of you who have a fool-proof method of leveling the reticle.