It is a must have tool for any pilot, and can measure rpm of any rotating object, such as all kinds of helicopters, fixed-wing airplanes with propellers and multi-copters. With high accuracy, fast response, compact size, ergonomic design and easy operation, this optical tachometer makes pilots have more fun! rpm range:700-4500rpm accuracy:â±1rpm power supply:cr2032 button battery weight :45g 10 level aperture adjustment 5 preset rpm value rotary dial for rpm value adjustment lcd display (sk-500010)