An instrument or machine for comparing anything to be measured with a standard measure; -- applied especially to a machine for comparing standards of length.

Bush's tape based-electronic cryptanalytic machines.

a device to magnify and precisely measure the projected image (shadow) of items normally difficult to measure such as soft products, or item with very irregular surfaces

A machine used for looking for parallax motion, proper motion, asteroids, or variable stars by quickly alternating between viewing two photographic plates from two different times.

A precise instrument which measures two dimensional plane coordinates from a vertical aerial photograph.