The Prochrono Digital Chronograph measure the velocity of almost anything that shoots with a large shooting area. Durable plastic light diffusers included. Accurate velocity measurement for rifles, pistols, arrows and shotguns. Easy to set-up and use with a HUGE shooting area. Store 9 shot strings with up to 99 shots per string in power down memory. Review through each velocity and shot data including standard deviation, extreme spread and average velocity. Delete an individual shot or entire string with the touch of a button. You can connect to the data port for remote capability with optional accessories. Quality Electronics, years of refinement yield a sensing design that is compatible with a wide variety of loads and light conditions. The velocity range is 21-7,000 feet per second and the temperature range is 32-100 degrees Fahrenheit. One 9-volt battery is required, not included. The device is accurate with +/-1% of measured velocity, or better. The mounting hole thread is 1/4 x 20 while the guide wire size is 3/16 x 16 inches.