This circular calculating rule is made of an aluminum disc 4-1/4" in diameter. The disc has a white plastic coating on both sides. There are two green transparent plastic indicators on the front and one indicator on the back. A metal screw and two supports hold the instrument together. The scales and markings are exactly like those on 1998.0119.01. A green synthetic leather case is marked in ink inside the flap: MATLACK.
The scales are also similar to those on 1979.0816.01, the Binary Slide Rule of Gilson Slide Rule Company of Stuart, Fla. Gilson manufactured slide rules under U.S. patent 1,404,019, issued to Clair A. Gilson for a "Mechanical Calculating Device" on January 17, 1922. The company was known for not putting its name on its products, which were resold by several American dealers of mathematical instruments.
The donor, Dr. Albert S. Matlack, purchased this object around 1942, when he was an undergraduate at the University of Virginia. He also used it as a research chemist at the Hercules Research Center in Wilmington, Del.
Reference: Accession file.
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