Concise Model 28 Circular Slide Rule

Concise Model 28 Circular Slide Rule

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Usage conditions apply
This white plastic circular slide rule was made by Concise Company, Ltd., of Tokyo, Japan, for Pan American Airlines. The base has a D scale, and there are C, CI, A, and K scales on a disc that rotates atop the base. A clear plastic indicator is pivoted at the center. The center of the rotating disc is marked: CIRCULAR CONCISE SLIDE RULE (/) NO. 28 (/) MADE IN JAPAN.
The back of the object is light blue with a white logo of a globe and is marked: WORLD'S LARGEST AIR CARGO CARRIER (/) PAN AM (/) WORLD'S MOST EXPERIENCED AIRLINE. The instrument was received with a clear plastic sleeve, a black vinyl case, and an undated instruction manual. The case is marked: Concise (/) No. 28. In 1963, the rule was advertised as "a revolutionary new design concept."
Concise has specialized in circular slide rules, particularly for promotional distribution by other companies, since its founding in 1949. The company operated under the name Concise Co., Ltd., which appears on the instruction manual, from 1959 to 1966, hence the rough date assigned this slide rule. The donor, industrial engineer Richard Freeze, reported that he received the item as a promotional item distributed at a conference. For other Pan American promotional slide rules, see 1996.3029.01 and 1996.3029.02. For other slide rules by Concise, see 1985.0636.02, 1996.0141.01, and 2006.0173.01.
References: "Concise Corporate History,"; Peter M. Hopp, Slide Rules: Their History, Models, and Makers (Mendham, N.J.: Astragal Press, 1999), 105; advertisement, Civil Engineering 33 (February 1963): 84; accession file.
Currently not on view
Object Name
calculating rule
slide rule
date made
Pan American Airlines
place made
Japan: Tōkyō, Tokyo
Physical Description
plastic (overall material)
paper (part material)
in case: 9.3 cm x 9.1 cm; 3 21/32 in x 3 19/32 in
overall: 8.2 cm; 3 1/4 in
ID Number
accession number
catalog number
Credit Line
Gift of Richard Freeze
Rule, Calculating
Promotional Item
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History
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I have the same Concise No 28 as James Taylor describes. The back has 38 different unit conversions in pie wedges. I always thought that was cool enough. But we just discovered that most of the conversion wedges have a code indicating how to set the rule. For example, to convert Miles to Kilometers There are 1.6093 kilometers per mile. The wedge says "87 opp 140". When you set 87 on the inner C scale opposite 140 on the D outer scale, you get 1.6093 kilometers per mile. Once it is set, you can read miles on the C scale and get kilometers on the D scale or vice versa...for any value of miles or kilometers. Same for most of the other conversions. The OPP settings are integer readings on both scales, so the owner does not have to estimate a decimal setting that leads to imprecision. A very helpful feature I never knew about.
I have one from the mid 60's in college. Memory does not place the source but it is a little different. The front matches your picture but the rear has a large number of English/Metric conversions, weight, distance, speed, etc. The small 17 page manual indicated is was made by the Concise Co., Ltd. in Edogawa-ku, Tokyo, japan. It came in a black plastic case marked, Concise (in script) No.28. It along with a 10" stick was used until I could afford a Scientific Instruments Co. no 1610-D, 5 in overall diameter, slide rule. I still carry both with me to show some of my college students what we used back before the internet came alive.

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