Automatic Arithmotor

James, Reuben R. · 1878

This U.S. Patent Office model for an adding machine has eight counting wheels that rotate on a common crosswise shaft. Around the edge of each wheel, the digits from 0 to 9 are printed repeatedly. Attached to each cylinder is a toothed revolving disc. The machine has a wooden case with a tin cover over the wheels. On the cover, next to each wheel, is a slip of paper labeled with the numbers from 1 to 9. To enter a number, one places one's finger at the tooth next to the digit on the appropriate paper slip, and rotates forward. The sum appears in slots in the metal cover, near the top of the machine. Each wheel has four cams linked to a weighted pawl-lever, which is responsible for carrying.