Concise 270 Circular Slide Rule

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This pocket-sized white plastic duplex circular slide rule has a clear plastic indicator that folds over the edge to serve both sides. It is held together with a metal pivot. The front base has L and D scales, with C, CI, A, and K scales on a sliding disc that fits inside the base. The center of the rotating disc is marked: CIRCULAR CONCISE SLIDE RULE (/) NO. 270 (/) MADE IN JAPAN. Near the center of both sides of the rule, the donor has scratched: SACK. The back base has DI and D scales, with S, T1, T2, and ST scales on the inset sliding disc.
The instrument was received with a clear plastic sleeve, a black vinyl case, and an undated instruction manual. The sleeve is marked: Concise (/) No. 270. As of 2012, Concise continues to manufacture plastic circular slide rules, including models 28N and 270N. The company operated under the name Concise Co., Ltd., which appears on the instruction manual, from 1959 to 1966. The donor, Michael Sackheim, reported that he purchased this rule for calculating during his school days but got little use out of it.
For other slide rules by Concise, see 1985.0636.02, 2003.0012.01, and 2006.0173.01.
References: "Concise Circular Slide Rule,"; accession file.
Currently not on view
date made
place made
Nihon: Kanto, Tokyo
Physical Description
plastic (overall material)
metal (part material)
overall: .1 cm x 11.6 cm x 11.5 cm; 1/32 in x 4 9/16 in x 4 17/32 in
ID Number
catalog number
accession number
Credit Line
Gift of Michael Sackheim
Rule, Calculating
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Slide Rules
Data Source
National Museum of American History


My Concise 270 has a few symbols around the "D " Scale whose meaning I cannot determine: at the +/-1.12 position a stylized "c "; at the +/-203 position a Greek rho symbol with a quotation mark; at the 344 position another Greek rho with a single quotation mark: at the +/- 573 position another rho mark wth a degree symbol over it. The last one I think I have determined that it represents the value of 1 radiant in degrees. The other rho symbols I think should be related to radiants or angles but I cannot make the connection. Please give me some clue as to what these symbols are used for. They do not appear on my K&E straight slide rules.ThanksDan Ellis

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