This product is mainly used for object acceleration and velocity measurement. Individual users can be used to measure the design speed of all kinds of playthings. Mini size is easy to carry. Simple and easy operation. Handheld type speed measuring instrument, with high accuracy measurement, 160 groups datas be recording. Measuring speed range: 1-999m/s. Metal and fully closed, this speed measuring instrument not affect by the sun and air current. High accuracy, with accurate measurement data. Humanized design unit conversion function. How to Use: LCD backlight setting, you can set constant light or long out. When you set as automatic, the screen light out after 10 seconds without operation. With automatic shutdown function. Charging by using the USB line, charging time is about 1 hour then you can use more than 10 hours after full charging. The red light bright in the charging and the blue light bright in full charging. Built-in overshoot , overdischarge , short-circuit , etc. Without using the pinboard, the using pipe diameter range is 20-31mm, less than 20mm you can add the pinboard or tie on the pipe. Using the pinboard, the using pipe diameter range is 16-43mm, less than 16mm you can add the pinboard or tie on the pipe. Included three keys, first is switch key also is confirmation key, second is up key, third is down key. Using semipermeable half-reflecting LCD screen that you can see clearly in the darkness or in strong light. Material:Metal + plastic colour:white Package Contents: 4 * Speed Measuring Instrument Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.