stereocomparator

from The Century Dictionary.

• noun An instrument, invented by Pulfrich in 1901, which utilizes the principle of the stereoscope in the comparison of pairs of photographs, as of a given stellar field, or of the sun, made by the same camera with a short interval of time between them. The stereocomparator optically superposes the two plates, and the images all lie apparently upon an even surface; but any object which has moved between the two exposures becomes at once conspicuous by apparently lying before or behind that surface.
• noun A stereoscope of greatly extended inter-objective distance by means of which it is possible to make exact measurements of the distances of objects pictured: used in topographical surveying.