Felsenthal FAE-5 Set Squares/Coordinate Scales, Group of 2

These two instruments are identical. On one side, each 4-3/8" white plastic L-shaped square has scales along its inner edge for reducing yards to the representative fraction (R.F.) of 1:25,000, divided to twenties and numbered by 500s from 0 to 1,500. Scales along its outer edge are for reducing yards to R.F. 1:50,000, divided to hundreds and numbered by thousands from 1,000 to 5,000. The end of one leg is marked: U.S. The other leg is marked: G. FELSENTHAL & SONS, INC. (/) MFR. PT. NO. FAE-5 (/) FSN 6675-283-0020. The letters FSN abbreviate "Federal Stock Number."
The other side is printed in red and 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 artillery or to interpret surveillance photographs. Compare to 1977.1141.17.
The Chicago firm that manufactured these squares was known as G. Felsenthal & Sons in the 1940s, G. Felsenthal & Sons, Inc., in the 1950s, and Felsenthal Instrument Co. in the 1960s and 1970s. It made model number FAE-5 for the U.S. Army from World War II through the 1960s. By the late 1960s, the product also came in an aluminum version.
Ben Wharton Rau (1904–1995) and his wife, Margery Felsenthal Rau (1916–2010), arranged the donation of this and many other instruments to the Smithsonian. Margery's grandfather, Gabe Felsenthal, founded the firm in 1899, and her father, Irving (1887–1956), was one of the "Sons" of G. Felsenthal & Sons. Ben worked for the Felsenthals for over three decades. His duties included touring military facilities with a large display of the company's products. He catalogued hundreds of instruments when the company went out of business in 1976. He also held patents on a collapsible film reel, a proportional divider, and a belt buckle assembly.
References: Deborah J. Warner, “Browse by Maker: Felsenthal,” National Museum of American History Physical Sciences Collection: Navigation , http://amhistory.si.edu/navigation/maker.cfm?makerid=173; "Irving G. Felsenthal," Chicago Tribune , February 26, 1956, http://www.susaneking.com/genealogy/showsource.php?sourceID=S01752&tree=GreenebaumSam; Copyright Office, Library of Congress, "Books and Pamphlets," Catalog of Copyright Entries , 3rd ser., 16, part 1, no. 2 (1964): 1392; ); Department of Defense, Employment of U.S. Army Aviation Company (Aerial Surveillance) in Counter-Intelligence Operations (February 9, 1966), D-1–D-2, http://www.dtic.mil/dtic/tr/fulltext/u2/371854.pdf; U.S. Army Artillery and Missile School, Artillery Trends, Instructional Aid No. 41 (Fort Sill, Okla., July 1968), 84, http://sill-www.army.mil/firesbulletin/archives/1968/JUL_1968/JUL_1968_FULL_EDITION.pdf; Ben W. Rau, "Collapsible Film Reel" (U.S. Patent 3,447,759 issued June 3, 1969), "Proportional Divider" (U.S. Patent D214,399 issued June 10, 1969), "Belt Buckle Assembly" (U.S. Patent 3,475,797 issued November 4, 1969.
Currently not on view
Object Name
set square
date made
G. Felsenthal & Sons, Inc.
Physical Description
plastic (overall material)
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
catalog number
accession number
Measuring & Mapping
Squares and Triangles
Science & Mathematics
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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