Gilson Binary Circular Slide Rule

This two-sided aluminum circular slide rule is coated with white celluloid enamel. The front has two interlocking yellow-green plastic arms, pivoted at the center with a metal nut and bolt with metal washers on both front and back. The back has one rotating arm. Thirteen circles of scales are on the front, including C (for multiplication, division, and proportion), CI (C inverted), A (squares), K (cubes), logarithms, a spiral log-log scale (marked from 1.0015 to 1,000,000), two binary scales for adding and subtracting fractions, a scale of drill sizes, a scale of thread sizes, and millimeters. The front is marked near the center: THE BINARY SLIDE RULE (/) MADE IN U.S.A. (/) COPYRIGHTED 1940.

Three concentric circles forming a scale of degrees, sines, and tangents are on the back. Inside this scale is a chart for decimal equivalents of fractions. The back is marked: COPYRIGHTED (/) 1931 (/) GILSON SLIDE RULE CO. (/) STUART, FLA. The sets of scales are almost the same as those on 1998.0119.01 and 1989.0032.01, which are both Gilson Midget circular slide rules, but the scale of thread sizes is in United States Form instead of United States Standard. Because it does not have alternating yellow and white stripes, this rule is unusual for a Gilson Binary slide rule. There is a case for this rule.

References: Sphere Research Corporation, "Gilson Binary/Atlas Circular Slide Rule Operating Information," http://www.sphere.bc.ca/test/circular-man2.html; Clippings Scrapbook, page 82, Cummings Library, Palm City, Fla.

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