Adders -- Circular Adders

Circular Adders

A collection of adders including a Magic-Brain Calculator, an Exactus Mini-Add, a Troncet Arithmographe, and a Locke Adder.

On some adders, numbers were represented along an arc of a circle. People used their fingers or a stylus to enter numbers. On a few of these instruments, a mechanism allowed one to carry a single digit. These objects are described here as adders with carry. They blur the line between adders and adding machines.