Burns Addometer
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 lever-set non-printing adding machine has wooden sides and metal covers for the back and the lower front. Four large toothed wheels are used for setting numbers, with five registering wheels in front and below these. Between each of the large wheels is a strip of metal; the digits from 0 to 9 are indicated along the edges of these strips. Each of the four right registering wheels is attached to a spur wheel with ten teeth that meshes with a large toothed wheel. Placing a finger in one of the teeth of a large wheel and rotating it forward advances the registering wheel proportionally. The number entered is visible in a row of windows at the front of the model. The four registering wheels to the left have on their left side a ring of ten equidistant pins that are used in carrying.
National Museum of American History’s own description
