Precision-machined, aircraft-grade aluminum instrument eliminates guesswork when adjusting your scope to fire at elevated, or very low targets. The orange needle moves with your rifle and displays a number that indicates the percent your rifle is off level. Multiply the indicated percent by the target distance to easily calculate the adjusted distance for gravity. Dovetailed bottom fits onto the aluminum mount (listed separately) which fits Picatinny and Weaver-style rails. Or, mount an extra Weaver-style ring on your scope tube and clamp the Indicator in the ring's dovetail. Ring not included. Lets you keep your face on the cheekpiece and see the Indicator. Mil-Spec version is waterpr Mfg: Sniper Tools Design Co. SPECS: Aircraft-grade aluminum, anodized, black. Cosine Indicator - 1" (2.54cm) diameter of dial, .75" (1.9cm) thick.