Hatfield Machine for Adding Numbers

Hatfield, Aaron L. · 1854

This patent model for an adder with mechanical carry has a wooden handle and circular base on which three concentric brass discs and a brass arm are mounted. The largest disc is glued to the base, and has the numbers from 1 to 99 indicated around the edge (there also is a blank space for zero). The middle and upper discs rotate about a central pivot, which has a smaller pin attached to it that holds the discs together. The middle disc is divided into 100 parts around the edge, with the parts numbered from 100 to 9,900 (again there is a blank division). The top disc has the numbers from 1 to 99 around the edge, as well as a blank. Next to each digit of the disc there is a small sunken tooth in the disc. A hole in the arm allows one to see numbers on the discs.