Metric Set Square

This 6-3/8" brass rule unfolds to form a set square. The outer edge of one leg has a centimeter scale numbered by ones from 1 to 16. It is marked: Nelle Mesure. The outer edge of the other leg has a scale for French inches (approximately 1-1/16") numbered by ones from 1 to 5. The first unit is divided into twelfths. The scale is marked: 6 Pouces. This leg has a pinhole for hanging a plumb bob and a rectangular hole with a rounded end (approximately 15/16" long) for viewing the plumb bob. The square has no maker's mark.
For a brief history of squares, see MA*316929. Typically, the legs were marked with scales for measuring lengths. What is unusual about this square is that it has both a traditional French measure and a unit from the newly introduced metric system, which is denoted as a "nouvelle mesure," or "new measure." The metric system was created in France in the 1790s, after the French Revolution of 1789. This suggests a date of about 1800 for the instrument.
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: "News From the Classes," Technology Review 21 (1919): 645; Albert Haertlein, Papers, HUG4444, Harvard University Archives, Cambridge, Mass.
Entry 1985.0580.05.
Currently not on view
Object Name
set square
date made
ca 1800
Physical Description
brass (overall material)
overall, folded: 16.2 cm x 2 cm x .4 cm; 6 3/8 in x 25/32 in x 5/32 in
place made
ID Number
accession number
catalog number
Drawing Instruments
See more items in
Medicine and Science: Mathematics
Measuring & Mapping
Science & Mathematics
Squares and Triangles
Metric System
Data Source
National Museum of American History, Kenneth E. Behring Center


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