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Filed: Sep. 23, 1899
Issued: Jan. 16, 1900
Inventor: Charles E. Keel
Looking for a ways to quickly and accurately calculate taxes, Charles Keel described his invention as follows:
"The invention consists in a manually-operated machine consisting of a pair of main rotating disks, one of which contains numbers representing valuations or base-figures and the other of which contains numbers representing results or amounts of taxes or percentage, a pair of rotating numbered disks to show the higher denominations or order of figures in connection with those on the main disks, intermediate gearing whereby the disks are caused to rotate in the proper ratios of speed to effect the desired results, and a frame whereby the several parts are supported."
Image taken from U.S. Patent 641,517 - Digitized by Google