"The Athlon Rangecraft Velocity PRO Radar Chronograph makes ballistic calculations easy. It uses Doppler radar to pick up your projectiles, eliminating the need to mount the Rangecraft to your weapon. This means it won't affect your zeroing or barrel harmonics so you get a truer picture of your ballistics without sacrificing accuracy. Since the Rangecraft isn't mounted to your gun and isn't triggered by muzzle blast, it works with suppressors, muzzle brakes, compensators, and more. Powered by an internal rechargeable lithium-ion battery, the Rangecraft is compatible with the Athlon Ballistics App. Measures velocity between 65 5,000 fps. IP67 waterproof rated. 2.4"" LCD screen. Uses Doppler radar to locate your projectile Won't affect zeroing or barrel harmonics Works with firearms with suppressors, muzzle brakes, etc. Measures velocity between 65 5,000 fps Works with the Athlon Ballistics App Internal rechargeable lithium-ion battery 2.4"" LCD screen IP67 waterproof rated"