Set Square Signed Chapotot

This 6-1/2" brass rule unfolds to form a set square. The outer edge of one leg has a scale for German inches (roughly 1-1/32 English inches), numbered by ones from 1 to 6. The first unit is divided into twelfths. The scale is marked: Demy pied de Rhin [half a foot of the Rhine]. The inner edge of this leg has a scale numbered by tens from -10 to 50. The first unit is divided into tenths. The scale is marked: Eschelle [scale]. This leg is also marked: CHAPOTOT A PARIS.
Both edges of the other leg have scales for French inches (roughly 1-1/16 English inches), numbered by ones from 1 to 6. The first unit on the outer edge is divided into twelfths. The leg is marked: Demy pied de Roy [half a foot of the French king]. This leg has a pinhole and a larger hole (1/4" diameter) for hanging plumb lines. Compare to 1985.0580.03, MA*316929, MA*317362, and MA*316914.
Louis Chapotot and his son, Jean, were prolific instrument makers with a workshop at Quay de l'Horloge du Palais à la Sphère Royale in Paris. Louis is known to have been active around 1670 to 1700, and Jean worked from about 1690 to 1721.
Albert Haertlein (1895–1960), who collected this square, graduated with a bachelor's degree in civil engineering from the Massachusetts Institute of Technology in 1918. He served in the engineering corps of the U.S. Army during World War I and taught engineering at Harvard from 1919 until 1959. Haertlein was prominent in the American Society of Civil Engineers.
References: J. A. Bennett, "New Acquisition: 'La planchette,'" Sphaera no. 9 (Spring 1999),; Adler Planetarium, Webster Signature Database,; "News From the Classes," Technology Review 21 (1919): 645; Albert Haertlein, Papers, HUG4444, Harvard University Archives, Cambridge, Mass.
Currently not on view
Object Name
set square
date made
Chapotot, Louis
Chapotot, Jean
Physical Description
brass (overall material)
overall: 16.5 cm x 2 cm x .5 cm; 6 1/2 in x 25/32 in x 3/16 in
place made
France: Île-de-France, Paris
ID Number
accession number
catalog number
Squares and Triangles
Drawing Instruments
Science & Mathematics
See more items in
Medicine and Science: Mathematics
Squares and Triangles
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Mrs. Albert Haertlein
Additional Media

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