Sliding Chart for Trigonometry - Triangulator

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This small sliding chart for teaching trigonometry shows formulae used to calculate angles, sides, area, sines, cosines and tangents in a right triangle. A plastic card slides in a sleeve that shows a right triangle on each side of it. Windows in the sleeve reveal letters of sides and/or angles of the triangle that are known, as well as a question mark for the side or angle to be found. Another window shows a formula that allows calculation of the unknown from the known. Thirty-two different formulae are listed on the two sides of the card.
One side of the chart has the mark: “Makes TRIGONOMETRY Easy”. It and the slide also are marked: “TRIANGULATOR” (/) P.O. BOX 4660 (/) WASHINGTON, D. C. The other side of the chart is marked: U. S. Pat. 2166372.
The chart and a pink leaflet giving instructions (1986.0441.02) fit in a small tan envelope. George E. Roeder copyrighted the term triangulator in 1936. He applied for a patent on June 16, 1938, and was granted U.S. Patent 2166372 July 18, 1939. The object is very similar but not identical to the patent drawing. Roeder (1895-1954) was born in Germany, became a naturalized U.S. citizen, was working as an instrument maker in Washington, D.C. in 1940, and would die in Buffalo, New York. An ad for the Triangulator appeared in the Hartford Courant in 1942. Advertisements for the instrument appeared in Popular Science as late as 1959, although by then it was distributed from Buffalo, New York.
According to the accession file, the donor had the Triangulator when he was an apprentice mechanic in about 1954.
Accession file.
George E. Roeder, “Formula-Finding Device,” U.S. Patent 2166372, July 18, 1939.
[Advertisement], Hartford Courant, August 9, 1942, p. 8. The Triangulator sold for 75 cents.
[Advertisement], Popular Science, 175, #6, December, 1959, p. 47.
Currently not on view
date made
ca 1954
Roeder, George E.
place made
United States: District of Columbia, Washington
Physical Description
plastic (instrument material)
paper (envelope material)
overall: .1 cm x 13.8 cm x 6.5 cm; 1/32 in x 5 7/16 in x 2 9/16 in
ID Number
catalog number
accession number
Credit Line
Gift of George A. Norton
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center


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