Jeffers 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 lever-set non-printing adding machine has a frame of two brown round end pieces joined by a central shaft and by two pieces of brass at the outside. The shaft carries six toothed wheels that may be rotated with the fingers. Each wheel has 30 teeth and is joined to a brass ring on its right. Around the rim of each ring is a slip of paper with the digits from 0 to 9 printed on it three times. One third of each ring is covered by a metal piece which has a window at the bottom and the digits from 1 to 9 engraved on it. To enter digits, wheels are rotated forward the distance indicated by these digits. Through the action of a carry mechanism, the total appears in the windows.
National Museum of American History’s own description
