Adders
Notched Band Adders

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

Building on ideas of Perrault and de Caze, in 1842 the Russian E. Kummer replaced the wooden rods on an adder with metal bands notched on each side. Kummer’s idea was adopted by the Frenchman Troncet, who published what he called an Arithmographe in the 1890s. Adders with notched bands became the most common form of the instrument sold in the United States in the 20th century.

These stylus-operated instruments generally had a crook at the top of each column, to allow one to move adjacent bands in carrying (or, in some cases, borrowing) a digit. They were manufactured around the world. Occasionally, notched band adders were combined with a slide rule, to ease multiplication and division. A special form of the instrument, designed for computer programmers, aided calculations in base 60 rather than usual decimal arithmetic.