The stadimeter is an optical rangefinder 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. The stadimeter uses a
system of mirrors, as in a sextant, to bring two images into coincidence. In
practice, a sailor would identify a distant ship, adjust the stadimeter for its
mast-head height (a figure available in published accounts), bring the image of
the mast-head into coincidence with the water line, and read the distance on the instrument’s drum. Stadimeters were widely used in World War I and again in World War II.
Ref: B. A. Fiske, "Method of and Apparatus for Range Finding," U.S. Patent #523,721.
"An Aid to Navigators. Lieut. Fiske’s Stadimeter for Determining a
Ship’s Exact Position," New York Times (Sept. 8, 1895), p. 28.
Instructions for the Use and Care of the Fiske Ship-Telegraphs and
Stadimeter (Published by Authority of the Bureau of Ordnance, Navy
Paolo E. Coletta, Admiral Bradley A. Fiske and the American Navy
(Lawrence: University of Kansas Press, 1979), pp. 38-40.
Peter Ifland, "Finding Distance–Part 1. The Fiske Rangefinders," Journal of Navigation 55 (2002): 147-152.