Japanese L-Square and Calipers

This 6-1/2" brass T-square is composed of two L-shaped brass pieces. The bottom piece slides along a groove in the long leg of the top piece. The outer edges on one side and the inner edges of the other side of all four legs are divided into units of 1-3/16" (3 cm). Each unit is thus roughly equivalent to the sun, a traditional Japanese unit of length that is 1/10 of a shaku, a "foot" measure. The units are subdivided into 50 parts. Whole and half-units are marked with zeroes.
The instrument was designed for measuring lengths, drawing right angles, and determining whether two lines are perpendicular to one another. When the two pieces are pulled apart, the instrument also functions as a caliper, to measure the width of a small object or the dimensions of part of a finished drawing. The English workshop of George Adams Jr. made a similar instrument from wood and brass in the late 18th century. Compare also to MA*261304 and to caliper rules such as MA*261299 and 1990.0099.01.
In 1876 the Japanese Empire Department of Education exhibited many instruments at the Centennial International Exhibition, a World’s Fair held in Philadelphia. After the exhibition, John Eaton, the U.S. Commissioner of Education, arranged for the transfer of Japan's entire exhibit to the Bureau of Education (then part of the Department of the Interior) for a planned museum. The museum closed in 1906, and much of the collection, including this object, was transferred to the Smithsonian in 1910.
References: William Ford Stanley, Mathematical Drawing and Measuring Instruments, 6th ed. (London: E. & F. N. Spon, 1888), 32–33; Howard Dawes, Instruments of the Imagination: A History of Drawing Instruments in Britain, 1600–1850 (The Dawes Trust Ltd., 2009), 80; "Caliper Rules," in A Source Book for Rule Collectors, ed. Philip E. Stanley (Mendham, N.J.: Astragal Press, 2003), 178–180; Japan. Department of Education, An Outline History of Japanese Education: Prepared for the Philadelphia International Exhibition, 1876 (New York: D. Appleton, 1876), 121–122, 191–202; U.S. Centennial Commission, International Exhibition, 1876. Reports and Awards, ed. Francis A. Walker (Washington, D.C.: Government Printing Office, 1880), viii:143, 335; U.S. Bureau of Education, Annual Report of the Commissioner (1876), ccxi–ccxii.
Currently not on view
Object Name
set square
date made
before 1876
Physical Description
brass (overall material)
overall: 16.8 cm x 8.8 cm x .4 cm; 6 5/8 in x 3 15/32 in x 5/32 in
place made
ID Number
accession number
catalog number
Drafting, Engineering
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Squares and Triangles
Data Source
National Museum of American History, Kenneth E. Behring Center


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