US Patent 7860673 Distance measuring device

Parallax is the apparent “shift” or “movement” of an object caused by a change in the position of the observer and is the phenomenon upon which the claimed invention operates. The invention is a mechanical device, comprising a viewing slide which has been marked with a series of markings, which is used to estimate the distance between an observer using the invention and an observed object within the field of view of the observer. When using the invention, the observer shall designate an observed object and take a series of steps using the invention. As a result of the parallax effect, the invention will then provide the observer with an estimate of the distance between the observer and the designated object.