Keeping your scope level is critical to long-range accuracy. Canting your scope, even just a couple of degrees, can cause a shift in the point of impact. If the scope isn’t level, dialing elevation or using reticle hold- over marks will throw your shot off. For long-range scopes, an anti-cant Indicator is a necessity.
HighPower Optics only sells anti-cant indicators that use spirit levels (that have a gas bubble). Solid ball levels are not sensitive enough to prevent canting errors at long range. Spirit levels have a sensitivity of 0.5 degree/mm of bubble movement. Keeping the bubble between the black lines during the shot will insure that canting errors won’t occur.