Concise 270 Circular Slide Rule

Description:

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," http://www.concise.co.jp/eng0731/circle02.html#02; accession file.