Stereoscopic rangefinder

A stereoscopic rangefinder uses two eyepieces and relies on the operator's visual cortex to merge the two images into a single picture.

[3] In November and December 1941, the United States National Defense Research Committee conducted extensive tests between the American Bausch and Lomb M1 stereoscopic rangefinder and the British Barr and Stroud FQ 25 and UB 7 coincidence rangefinders, and concluded "that the tests indicate no important difference in the precision obtainable from the two types of instrument – coincidence and stereoscopic.

They do indicate, however, that the difference in performance between large and small instruments is by no means as great as would be anticipated from simple geometrical optics.

The angle of sight of a rangefinder and the range to the target can be combined in a simple computer to produce a measurement of altitude.

The resulting instrument becomes a combined height-finder/rangefinder and was standard equipment for land and naval based anti-aircraft units.