Laser Chronograph uses the principle of laser ranging. Laser distance measurement (ie, the speed of 300,000 km / s) is to determine the distance between the measured object and the test point by transmitting the laser beam to the measured object and receiving the reflected wave of the laser beam and recording the time difference The Laser measuring instrument on the measured object twice with a specific time interval of laser ranging, to obtain the distance in the measured object within the distance, so as to get the moving speed of the measured object.