Rangefinder is a tool to measure the distance between the observer and the target or object being observed. There are several rangefinder working methods, some are based on sonar, laser, or radar. The working principle of the Rangefinder is the laser beam emitted by this tool to the object, and the time the object reflects this beam back to the rangefinder will be calculated to determine the distance to the object displayed on the screen. This tool uses 9 volt battery power for Bushnell and 3 volts for Nikon laser.