Engineering Instruments 250-V Simplex Slide Rule

This ten-inch, one-sided wooden slide rule is coated with white plastic on the front face and both sides of the slide. A, D, and K scales are on the base. B, CI, and C scales are on one side of the slide, with S, L, and T scales on the other side. The indicator is clear frameless plastic. The top of the base is marked: MADE IN U.S.A. It is also marked: ENGINEERING INSTRUMENTS, INC., PERU, INDIANA. It is also marked: PAT. PEND. The right end of the slide is marked: 250-V. Tables for equivalents and conversions appear on the back of the instrument. The rule fits in a tan paper sleeve—neither the original simulated leather case nor the instruction manual were received with the instrument.
Vivian (Breyer) Lawrence received Lawrence Engineering Service, a manufacturer of slide rules in Peru, Ind., in her divorce from George Lee Lawrence in 1947. Her new husband, Frank Bozarth, was president of the renamed Engineering Instruments, Inc., until the company burned down in 1967. Although the building was insured, Engineering Instruments never rebuilt. This rule probably dates between the late 1950s and 1967. The model number may mean that the rule is 250 mm long with a veneered finish, although the scales are actually about 255 mm. The rule sold for $2.00. Compare to 1983.0042.01.
References: Bruce Babcock, "Lawrence Engineering Service — A Tale from an American Small Town," Journal of the Oughtred Society 5, no. 2 (1996): 55–61; David G. Rance, "The Unique Lawrence," Proceedings of the 17th International Meeting of Slide Rule Collectors (September 2011), 87–107,; Peter M. Hopp, Slide Rules: Their History, Models, and Makers (Mendham, N.J.: Astragal Press, 1999), 195–196.
Currently not on view
Object Name
slide rule
date made
ca 1958-1967
Engineering Instruments, Inc.
Lawrence Engineering Service
Physical Description
wood (overall material)
plastic (laminate and cursor material)
paper (case material)
overall: .9 cm x 28.9 cm x 5.9 cm; 11/32 in x 11 3/8 in x 2 5/16 in
place made
United States: Indiana, Peru
ID Number
accession number
catalog number
Science & Mathematics
Rule, Calculating
Slide Rules
See more items in
Medicine and Science: Mathematics
Slide Rules
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Gift of Terry M. Sachs
Additional Media

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