Keuffel & Esser 68-1210 Log Log Duplex Slide Rule

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This ten-inch duplex slide rule is made from mahogany coated with white celluloid and is held together with metal end pieces. The indicator is glass with plastic edges held together with metal screws. One side of the base has LLO1, L, K, A, D, DI, and LL1 scales, with B, T, SRT, and S scales on the slide. The left end of both parts of the base is marked: 092, and the left end of the slide is marked: 991092. The other side of the base has LLO2, LLO3, DF, D, LL3, and LL2 scales, with CF, CIF, CI, and C scales on the slide. The right side of the slide is marked: © (/) K+E. This form of the K&E logo dates to 1949.
The top edge of the rule is marked: PATS. PEND.; MADE IN U.S.A; 68 1210 LOG LOG DUPLEX DECITRIG ®; COPYRIGHT 1947 BY KEUFFEL & ESSER CO.; PATS. 2,500,460 2,168,056 2,170,144 2,285,722 2,422,649. The rule has a green leather case marked on the flap: K+E. Inside the flap is written in ink: Howard (/) Ebenstein; Pratt (/) Institute (/) 1965. Howard Ebenstein acquired this slide rule as a student in mechnical engineering at Pratt Institute in New York City. He went on to a career in public service with the the Department of the Navy, Peace Corps, and the District of Columbia Energy Office.
Keuffel & Esser of New York converted its model numbers to the 68 series in 1962. It advertised the model 68–1210 in its 1962, 1966, 1967, and 1972 catalogs. In 1962, the rule came with a case with a belt loop and a hardcover manual. By 1967, there was an option to purchase the rule with a case without a belt loop and a softcover manual. Thus, this example was probably produced closer to 1965 than to 1962. The serial number is also consistent with this date. For earlier versions of this slide rule, sold as the model 4081, see MA.318482, MA.334387, 1990.0687.01, and 1986.0790.03. For instructions, see 1987.0085.02.
References: Clark McCoy, ed., "K&E Catalogs and Price Lists for Slide Rules,"; Wayne E. Feely, "K & E Slide Rules," The Chronicle of the Early American Industries Association 49, no. 5 (June 1996): 50–52.
Currently not on view
date made
Keuffel & Esser Co.
place made
United States: New York, New York
Physical Description
mahogany (overall material)
celluloid (laminate material)
glass (cursor material)
metal (part material)
leather (case material)
overall: 2.2 cm x 33.4 cm x 6.7 cm; 7/8 in x 13 5/32 in x 2 5/8 in
ID Number
accession number
catalog number
Credit Line
Gift of Howard Ebenstein
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History


"Guys:I am the donor of this slide rule. I can confirm that it was acquired (as a gift from my father) while a freshman in mechanical engineering at Pratt Institute, from which I graduated with a BS in 1969. The last name on the inside flap is not Eberstein but rather Ebenstein; perhaps part of the letter "n " became worn, as I don't think I would have spelled my name incorrectly :). By the way, the owner's manual (stiff soft cover, as I recall) was donated along with the slide rule and case. It's pretty cool to have donated this calculating device, which I took pride in owning and using, and have it preserved and valued so that it can be appreciated by others. Keep up the good work!"

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