Patent Model for an Adder with Carry Invented by George Farmer

This patent model for an adder has three concentric, linked discs that revolve on a central pivot. The bottom disc is numbered from 1 to 99 clockwise around its toothed edge, to represent hundreds and thousands. Above it is a smaller disc, also with teeth around the edge, numbered from 00 to 99 clockwise to represent units and tens. A window in the third, top, largest disc shows the result on the dials below. The largest disc is numbered from 1 to 100 around the edge. Atop this disc is a rotating arm. Moving the arm counterclockwise advances the inner disc proportionally, allowing one to enter numbers up to 99.
A lever extends from the side of the disc and bends over the top. If the arm rotates around a full 100 units, it pushes this lever, causing a carry. The lever also may be used to zero the hundreds and thousands digits. See U.S. patent 69,647 for “Improvement in Tallying Instrument.” According to the patent, the invention “relates to a new and improved method of registering or tallying the quantity of lumber measured, or keeping account of sums of money paid out or received . . .”
There was a George Farmer (born about 1831 in England, died 1880 in Saginaw, Michigan) who worked as a miller and shingle maker in Illinois and in Michigan. He is listed in the 1860 U.S. Census as living in Elmira in Stark County, Illinois, working as a miller. That same year he received a patent on August 21for an improvement in harvesters (#29685). By 1870, he was living in Saginaw, Michigan, still working as a miller. In the 1880 Census he is listed as a shingle manufacturer. He and his son, Albion, ran a shingle-making business in Saginaw under the name of George Farmer & Son. It is listed in the 1878 city directory for the town. The George Farmer who received the patent for this adder was a resident of Flint, which is near Saginaw.
Reference: George Farmer, “Improvement in Tallying Instrument,” U.S. Patent 69,647, granted October 8, 1867.
Currently not on view
Object Name
adder with carry
date made
Farmer, George
Farmer, George
Physical Description
brass (overall material)
overall: 1.2 cm x 10.7 cm x 10.7 cm; 15/32 in x 4 7/32 in x 4 7/32 in
place made
United States: Michigan, Flint
place patented
United States: Michigan, Flint
ID Number
accession number
catalog number
See more items in
Medicine and Science: Mathematics
Science & Mathematics
Data Source
National Museum of American History, Kenneth E. Behring Center


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