Laser range finders are a pretty impressive piece of technology. These devices use a bean of photons to determine the distance to a specific object or land point. Almost every laser range finder out there operates off of the “time of light” principle, which is simply a measurement of the amount of time it takes for a photon to reach the target, reflect off, and return to the range finder.
Because the speed of light is a constant, it is pretty easy for the onboard computer to convert the time of light into an accurate estimation of the amount of distance between you and your target.