The AR891 rangefinder is an instrument that uses laser to accurately measure the distance to a target. The laser rangefinder emits a very thin laser beam towards the target during operation, and the reflected laser beam is received by the photoelectric element. The timer measures the time from emission to reception of the laser beam and calculates the distance from the observer to the target. Laser rangefinders are lightweight, small in size, easy to operate, fast and accurate, with an error of only one-fifth to one hundredth of other optical rangefinders. Therefore, they are widely used for terrain measurement, battlefield measurement, tank, aircraft, ship and artillery ranging of targets, measuring the height of clouds, aircraft, missiles, and artificial satellites. It is an important technical equipment for improving the accuracy of high tanks, aircraft, ships, and artillery.