One inscription on this celluloid rule reads “COPYRIGHT G. P. WILHELM 1917 / MFR. AND DISTRIBUTOR EDWARD C. MCKAY / CLEVELAND, OHIO / PATENT APPLIED FOR.” Another reads “THE MILOMETER.” Glenn Perrin Wilhelm (1889-1941) was an officer in the U.S. Army, and an authority on ballistics. He devised this slide rule-like computer for forward observers, to help them direct the indirect fire of machine guns and small arms.
Ref: Glenn P. Wilhelm, Machine Gun Fire Control (Cleveland: Edward C. McKay, 1917).
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