Specifications: RPM Range:700-4500RPM Accuracy:＋/- 1 RPM 10 Level Operature Adjustment 5 Preset RPM Value Rotary Dial for RPM Value Adjustment LCD Display Power Supply:CR2032 Button Battery Weight:45g Optical Tachometer 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! How it works As we know when the flashing frequency of 3D Glass Screen is the same as the RPM of a rotating object if we view the rotating object through the 3D Glass Screen the rotating object is "static". At this time the flashing frequency of 3D Glass Screen is the RPM of this rotating object. When we view the rotating blades through the 3D Glass Screen if the blades is"static" the flashing frequency displayed in the LCD is the RPM of this blades. Applied for all kinds of helicopters fixed-wing airplanes with propellers and multi-copters. 5 presets of Flashing Frequency/RPM The RPM range that the Optical Tachometer could test is from 700RPM to 4500RPM. In order to make it convenient for you to enter close RPM and find out the exact RPM in a short time 5 presets of RPM can be saved in this unit and you could enter any preset by pressing "F" key. Each preset RPM value can be set according to your different helicopters and airplanes and also the last RPM value before shutting off will be saved as preset. 10 Level aperture adjustment As the back light of the rotating object is quite different there are 10 levels of aperture which can be set by pressing "F" key. In this caseyou could capture clear image through the 3D Glass Screen whether the light is bright or dark so that you can get accurate RPM value of the rotating object.