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The Binary Circular slide rule was produced in the United States by the Gilson Slide Rule Co. since 1930. It was fabricated on a 8.25 inches circular aluminum plate coated with white celluloid enamel where scales were printed, and it has three movable transparent celluloid cursors, two on the front face and one on the back, screwed at the disk center. It was a very popular model that was commercialized under other brands like Dietzgen, Compass, Brunnig, Post and Lutz. Gilson Slide Rule Co. was sold in 1960, and I have not found information about the new owner and if they continued the production of this rule.
The elaborated design of the thirteen front scales on these rule was done by Richard Gilson by 1935 when he was 18 year old. This was in impressive achievement not only for the designer's short age, but also for the scales included: C (for multiplication, division, and proportion), CI (C inverted), A (squares), K (cubes), a spiral log-log scale ranging from 1.0015 to 1,000,000 (~29 inches long!), two binary scales for adding and subtracting fractions, a scale of drill sizes, a scale of thread sizes, and millimeters. The back face was the same of the Atlas Calculator: three concentric circles forming a scale of degrees, sines, and tangents, and a chart for decimal equivalents of fractions. With all these scales the Binary Rule was very well suited for Science and Engineering applications.
The Binary circular was also fabricated in a 4.25 inches version called the Commercial Calculator, since 1919, with the special capacity to determine the amount of interest from interest rates and dates. On the front face there is a C scale, CI scale, a scales of logarithms base 10, a scale of squares, a "binary" scale, a spiral log-log scale (~9.4 inches long), a scale for the decimal equivalent of fractions, a scale of drill sizes, and a scale of thread sizes. On the back face the same trigonometric scales and fraction-decimal table conversion as on the 8.25 in version.
Same as other brands, these rules have no serial number or other information to determine the exact fabrication year. Only is shown the years the designs were patented: 1931, 1940 for the 8.25 inches rule, and 1931, 1936 for the 4.25 inches rule.
Above are shown two 8.25 inches unbranded specimens, same model but fabricated about thirty years apart, the oldest possibly fabricated in the early 1930"s, the newest fabricated in the 1960's, and commercialized not only by Gilson but also by Compass, Dietzgen, and Brunning.
Below are shown the 8.25 inches and the 4.25 inches versions. I assume that the 4.25 inches were also fabricated in the 1930's:
Below are pictures of a 4.0 inches item fabricated in the early 1920's, this one with the brand Gilson on. This model, copyrighted in 1919 and patented in 1922, shows some differences with the model copyrighted in 1931. The scales on the front face are: C, CI, L, A, Binary (paired with the A-scale to convert fractions of an inch into decimals with the first half of A-scale, and integer+fraction inches into integer-decimal with the second half of A-scale), LL (Spiral), Fractions (paired with L-scales for fractions of an inch to decimal conversion), Drill Scale (1/2 turn), Thread Scale (1/2 turn) Binary, Fraction, Drill, Thread, Millimeter.
On the back face: Sin/Cos, Degrees, Tan/Cot, Fraction of an inch-Decimal Equivalent. The Trigonometric scales in this 1922-model are not split as in the 1931-model, but are different to others I have seen: scales subdivisions run on a different concentric circle, and in some way make readings easier.
These rules were kind of affrodable in those years. The Midget 4.5 inches diameter was offered, in 1938, for $2.00 (about $43 USD in 2023), price including "instructions and heavy fabrikoid case".
The next problems can be solved with a precision of two-three decimals using the Binary Midget Rule:
SRPractice-1.pdfHere is the scan done by the International Slide Rule Museum of the original Gilson User Manual for the Binary Slide Rule:
gilson-manual.pdfClick on the next links to see professional panoramic pictures of the Midget models.
Click on the next links to see professional panoramic pictures of the Midget models.
References:
Alice L. And Greg E. Luckhardt: Historical Vignettes - Gilson's Circular Slide Rule Company. TCPalm. January 12, 2012. http://archive.tcpalm.com/yournews/martin-county/historical-vignettes---gilsons-circular-slide-rule-company-ep-383231720-343533252.html?fbclid=IwAR2kQyhLj6u7nT0x6NRTUb_J_7_RBKofiToCPFPxNOBr_QI4YM1PtLWlgj0
Aldinger, Henry - Chamberlain, Ed: Gilson Slide Rules - Part 1 - The Small Rules. Journal of the Oughtred Society. Vol 1, No. 1, Spring 2000, pp. 48-60. https://osgalleries.org/journal/pdf_files/9.1/V9.1P48.pdf
Circular Slide Rule. Video with the basic operations of the circular slide rule: https://www.youtube.com/watch?v=7IQgrF2c8SI
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