Speed Gun is a tool in extended set of the Smart Tools collection (speedometer). This app measures the speed of a moving object by touch like a velocimeter. Usage is easy: To measure the speed, input the shortest distance to the target, and touch the screen following target. Please measure the target distance in advance with a range finder tool (e. g. Smart Distance, Smart Measure). It supports most android devices with rear camera. If the result is not accurate, you can calibrate your device with the [Speed Calibration]. Do you want more tools? Get [Smart Distance Pro]For more information, see the manual, Youtube video and the blog. Thank you.