Stadimeter

thumb|alt=A handheld stadimeter|200px|right|A stadimeter operator adjusts the lower knob until the top and bottom of the object are aligned, and then reads the corresponding range off the edge of the lower knob through a small magnifying lens. A stadimeter is an optical device for estimating the range to an object of known height by measuring the angle between the top and bottom of the object as observed at the device. It is similar to a sextant, in that the device is using mirrors to measure an angle between two objects but differs in that one dials in the height of the object. It is one of several types of optical rangefinders, and does not require a large instrument, and so was ideal for hand-held implementations or installation in a submarine's periscope. A stadimeter is a type of analog computer.

==Development and use== thumb|alt=A handheld stadimeter|200px|right|A Mk 5 Mod 0 US Navy Stadimeter made in 1942 by Schick Inc. of Stamford CT. The hand held stadimeter was developed by Bradley Allen Fiske (1854–1942), an officer in the United States Navy. It was designed for gunnery purposes, but its first sea tests, conducted in 1895, showed that it was equally useful for fleet sailing and for navigation. It was normally kept on the bridge and used from there and on the bridge wings to keep warships at the proper distance from one another when steaming in formation and for use in convoys.