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Filed: Oct. 5, 1899
Issued: Oct. 16, 1900
Inventor: Chester W. Brown
In his patent, Brown described his invention as follows:
"This calculator consists of three circular disks 1 2 3, made of any suitable material, each being of different size from the other and mounted one upon the other, the smallest one being in front. These disks are secured together by a central rivet 4, which serves as a common pivot around which each disk can revolve. The exposed edges of these disks are each provided with a circumferential space having radial graduations 5 5-1 5-2, those on each disk containing figures and letters different from those on either of the others, and by rotating the disks different combinations are obtained to produce the calculations desired."
Image taken from U.S. Patent 659,727 - Digitized by Google