Invented by Leonardo Torres in 1920, the Torres calculating machine is a machine that solves essential addition, subtraction, multiplication, and division problems using a simple manner. It was a ...

This full-keyboard, non-printing calculating machine has a metal frame painted black, with metal handles on each side. The nine columns of color-coded black and white digit keys each have a red ...

In 1875 Frank S. Baldwin of St. Louis patented a pinwheel calculating machine. He manufactured a few of these machines, but they did not sell well. Baldwin went on to take out a number of other ...