Mengshen Digital Tachometer, 2 in 1 Non-Contact & Contact Tach Rotation Speed Measurement RPM Meter, M522 Contact Measurement Range: 2~ 20,000 RPM Non-contact Measurement Range: 2~ 99,999 RPM Resolution Ratio: 0.1 or 1 Accuracy: +/-(0.02%) + 2 digit REV Measuring Range: 1-99999 Sampling Time: 0.5sec Measurement Distance: 50mm ~ 600mm Display: 5-digit Backlight LCD Display Working Temperature: 0C-50C(32F-122F) Power Consumption: 45mA Power Supply:9V DC Battery(Included) Sensor LCD display Mode key Memory view key Backlight key Measuring key Battery compartment Open battery cover by screwdriver, install a 9v battery, Cut a square off from the reflective tape and paste it on the object to be measured, Press &#034;MEAS&#034; button to aim the reflective tape with laser. Install the adapter on the instrument, aim on and contact the axis of the object measured, then the data will display on the LCD screen. Before using, you can practice or test it on conduction motors. Usually keep device close to the object measured to reduce the size of thelaser dot can get a more accuratereadings. The purpose of the reflective tape is to offer a good contrast between background and measuring area, but if the part measured has other reflective surfaces, like shiny metal, please apply a non-reflective tape(black or a dark color tape) to act as background. If reflective tape ran out, white paint is an easy substitute for it.