Wheeler Engineering Anti-Cant Indicator, Pic Rail Indicates precise, repeatable level gun position Increases accuracy by insuring proper gun alignment Easy-to-view from shooting position Attaches to any Pic Rail and aligns with precision-leveling set screw Folds in when not in use Precision machined aluminum with anodized finish Keeping your scope perfectly aligned is critical to long-range accuracy. Canting your scope, even just a couple of degrees, can cause error in point of impact. With modern "Drop-Compensating" scopes, an Anti-Cant Indicator is a necessity. If your gun isn't aligned correctly dialing up the turrets or using hold-over marks, will just throw your shot off. This error can easily be enough to cause misses. The Wheeler Anti-Cant Indicator ensures that your rifle is always held near perfectly vertical, eliminating any chance for "Cant Error" to cause a miss. The Indicator reveals precise, repeatable level gun position and increases accuracy by insuring proper gun alignment - critical for turret adjustment and hold over for bullet drop compensation Easy-to-view from your shooting position, the Indicator attaches securely to any Pic Rail and is tunable with the precision leveling set screw.