While trying to explain the meaning of the carry digit during addition an subtraction to my oldest son, I’ve given him a nice little device to play with: the Addifix-9 number cruncher.

I’ve briefly mentioned this device before in a post. This time I’ve made a short video about the mechanical calculator in action and present more details:

In the 1950s/60s The Addifix series was sold as “Addifix-9 Taschenrechenmaschine” by the German mail-order company Neckermann. Its predecessor was the Addiator from Carl Kübler which was sold since the early 1920s  [Source: sliderulemuseum.com]. The underlying mechanical principle is quite old (an documented example is the mechanical calculator by Claude Perrault from the 17th century).

The Addifix is a pocket-sized (13 x 9 cm) slide adder that can be used from both sides – one side for addition and one for subtraction. The slides (one for each digit) are handled with a metal stylus.