Plotting Board M10, Felsenthal Instruments Company Model FAO-6

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Soldiers in the U.S. Army infantry used devices like this to plot the relative position of guns, base points, and targets. A plastic rotating disc pivots on a flat plastic base. The base is square on one side and semicircular on the other. Printed in red on the base, directly under the disc, is a rectangular grid of lines. Numbers on the grid (moving out from the center of the disc) range from 0 to 19, representing hundreds of yards. Each small grid square thus represents 50 yards on a side (or, if one uses a scale to the left of the first one, 100 yards on a side).
To plot directions, one uses a scale on the edge of the disc which is divided evenly in mils from 0 to 6400, with every 10 units marked and every 100 units labeled (the labels go from 0 to 63). A vernier along the top edge of the base allow for further subdivision. Having measured the distance and azimuth of both a gun and a target, one can find the distance between them (the range required) and the direction in which the gun should be aimed.
A mark on the upper right of the base reads: BOARD, PLOTTING (/) M10. Also on the top edge of the base is a scale of centimeters divided to millimeters. Along the right edge of the base is a scale of inches divided to tenths of an inch.
The instrument fits in a cloth case.
This example of the M10 was made by Felsenthal and had Felsenthal model number FAO-6. According to a tag received with the object, it dates from 1948.
Compare 1977.1141.13 and 1977.1141.14.
Accession File
U.S. War Department, War Department Field Manual FM23-55, Browning Machine Guns. . ., 1945, pp. 270-275. This is a description of the M10 plotting board.
Currently not on view
date made
ca 1948
Physical Description
plastic (overall material)
metal (pivot; snap material)
cloth (case material)
overall: .3 cm x 22.2 cm x 22.4 cm; 1/8 in x 8 3/4 in x 8 13/16 in
ID Number
catalog number
accession number
Credit Line
Gift of Ben Wharton Rau and Margery Felsenthal Rau
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Plotting Boards
Data Source
National Museum of American History


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