Stadiametric rangefinding

Soldier observed at 400 m: The stadiametric rangefinder in the bottom-left corner of the PSO-1 telescopic sight reticle can be used to determine the distance from a 1.70-meter (5 ft 7 in) tall person or object from 200 m (bracket number 2 to the right) to 1,000 m (bracket number 10 to the left).

Stadiametric rangefinding, or the stadia method, is a technique of measuring distances with a telescopic instrument. The term stadia comes from a Greek unit of length Stadion (equal to 600 Greek feet, pous) which was the typical length of a sports stadium of the time. Stadiametric rangefinding is used for surveying and in the telescopic sights of firearms, artillery pieces, or tank guns, as well as some binoculars and other optics. It is still widely used in long-range military sniping, but in many professional applications it is being replaced with microwave, infrared, or laser rangefinding methods. Although much easier to use, electronic rangefinders can give away the shooter's position to a well-equipped adversary, and the need for accurate range estimation has existed for much longer than electronic rangefinders small and rugged enough to be suitable for military use.