Speed Gun is a tool in extended set of the Smart Tools collection (speed).This app measures the speed of a moving object by touch like a velocimeter.Usage is easy: To measure the speed, input the closest distance to the target, and touch the screen following target. With a range finder app(e.g Smart Distance, Smart Measure), measure the target distance in advance.There are too many android devices in the world. If yours is inaccurate, you can calibrate it by yourself.* Do you want more tools?Get [Smart Distance Pro]For more information, see the manual, Youtube video and the blog. Thank you.