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:±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)