Hill Arithmometer
From the collection of National Museum of American History. Free to download, adapt and use — no permission needed.
This U.S. Patent Office model for an early key-driven adding machine has a wooden case with two columns of keys. Each column has six wooden keys. At the back are two wooden discs. Around the edge of each disc is a paper slip with the digits from 0 to 9 printed. These digits repeat seven times on each disc. To the right of each digit is, in smaller type, its nines complement, which is used in subtraction and division. Each wheel of the machine has attached to its side a ratchet that rotates according to the motion of a pawl. The base of the pawl is attached to the end of a lever that extends forward the length of the machine and is pivoted near the front. Above each lever, on the outside of the machine, is a column of keys, numbered from 1 at the top to 6 at the bottom.
National Museum of American History’s own description
