Ballou Adding Machine
From the collection of National Museum of American History. Free to download, adapt and use — no permission needed.
This U.S. patent model for a non-printing lever-set adding machine has a metal casing painted black and a wooden bottom. The curved front of the machine has slots for six movable rings. The part of the case to the right of each ring is marked with the digits from 0 at the bottom of the curve to 9 at the top. A crosswise shaft in the machine carries a series of six toothed metal rings that fit between the openings in the case and serve as finger wheels, ratchets, and registers. The rings are sufficiently thick so that digits can be inscribed around their edges, next to the teeth. One digit of each wheel is visible at the top of the machine, showing the result when numbers are entered by turning rings forward. The left side of each ring has a pin every ten places, which drives the adjacent wheel when carrying is required.
National Museum of American History’s own description
