Brunsviga calculating machine, c 1950.
© Science Museum / Science & Society Picture Library
Barrel calculating machines were smaller, lighter and easier to operate than their predecesors, Arithmometers. The machine performs multiplication by repeated addition and included the wheel with a variable number of teeth as patented by Willgodt T Odhner (1845-1905) in 1891. Odhner sold the German patent to Mesrs Grimme, Natalis & Co.