Felsenthal FAE-6 Set Square/Coordinate Scale

Description
On one side, this 4-3/8" white plastic L-shaped square has scales along its inner edge for reducing yards to the representative fraction (R.F.) of 1:20,000, divided to twenties and numbered by 500s from 0 to 1,000. Scales along its outer edge are for reducing yards to R.F. 1:62,500, divided to hundreds and numbered by thousands from 1,000 to 6,000. The end of one leg is marked: U.S.
The other side has scales along its inner edge for reducing meters to R.F. 1:25,000, divided to twenties and numbered by 500s from 0 to 1,500. Scales along its outer edge are for reducing meters to R.F. 1:50,000, divided to fifties and numbered by thousands from 1,000 to 5,000. The end of one leg is marked: U.S. The device, also known as a "coordinate scale," was used by soldiers to compare measurements to notations on a chart in order to aim weapons. Compare to 1977.1141.16. This example was also received with a duplicate square, but the second square was broken and discarded.
According to the accession file, this instrument was made for the U.S. Army by Felsenthal Instrument Company in 1945 as model number FAE-6. The company was the leading supplier of mathematical instruments to the U.S. Army Air Force and the U.S. Navy Bureau of Aeronautics, particularly during World War II (when the firm was known as G. Felsenthal & Sons). After the company ceased operations in approximately 1976, it provided a large sample of its products to the Smithsonian. The lack of any form of the firm's name on this instrument suggests it may actually have been made in the 1960s. For company history, see 1977.1141.02.
Location
Currently not on view
Object Name
set square
date made
ca 1945
maker
Felsenthal Instrument Co.
Physical Description
plastic (overall material)
Measurements
overall: .1 cm x 11.2 cm x 11.2 cm; 1/32 in x 4 13/32 in x 4 13/32 in
ID Number
1977.1141.17
catalog number
336401
accession number
1977.1141
subject
Measuring & Mapping
Squares and Triangles
Science & Mathematics
Mathematics
Artillery
Metric System
See more items in
Medicine and Science: Mathematics
Squares and Triangles
Metric System
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Ben Wharton Rau and Margery Felsenthal Rau
Additional Media

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