Charvoz-Roos SR-105D Simplex Slide Rule

This one-sided wooden rule is faced with white celluloid and has a plastic indicator and metal endpieces. The base has A, D, and K scales; B, CI, and C scales are on the front of the slide, and S, L, and T scales are on the back of the slide. The back of the slide is visible on the back of the rule, but the back of the base has tables of equivalents instead of scales. So, the slide must be removed from the rule, turned over, and reinserted to use the S, L, and T scales with the A, D, and K scales. (There is, though, a hairline on the back of one endpiece for using the S, L, and T scales by themselves.) The tables of equivalents indicate how the slide should be set on the front to convert various units, such as centimeters to meters. The instrument fits in a brown synthetic leather case. The front of the base is marked: SR-105D CHARVOZ-ROOS MADE IN U.S.A. The back of the base is marked: ACU (/) DESIGN (/) PAT. PENDING.

Andre Charvoz (1892–1969) and his partners began to sell rebranded slide rules as well as slide rules assembled from parts in East Rutherford, N.J., around 1939. The company was called the Charvoz-Roos Corporation from 1946 until 1953, when it went bankrupt. The scales on the celluloid layers were apparently provided by the Acu-Rule Mfg. Co. of St. Louis, Mo., which either used Acu-Design as a brand name or as a separate business that supplied scales to other manufacturers. Acu-Rule's president, Wilfred Boos, applied for a patent on this rule in 1949 and received it in 1952.

References:

"Time Line for Charvoz-Roos Slide Rules," International Slide Rule Museum, http://sliderulemuseum.com/SR_Dates.htm#

Charvoz; Wilfred J. Boos, "Slide Rule" (U.S. Patent 2,594,897 issued April 29, 1952).

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