Calculator

Schickard, a German professor and Protestant minister, seems to have been the first to create an adding machine in the 1620s. It performed addition, subtraction, and carrying through the use of gears and preset multiplication tables. The machine only computed numbers up to six digits. Once the operator surpassed this limit, he was required to put a brass ring around his finger to remind him how many carries he had done. Schickard made sure to include a bell, so that the user would not forget to add his rings. His drawings of the machine were lost until the mid-1960s when a scrap of paper was located inside a friend's book which had a drawing of his machine. With this drawing and Schickard's letters, a reconstruction was made in 1971 to honor the adding machine's 350th anniversary.

Finished in 1642, Blaise Pascal's calculating machine also automatically carried tens and was limited to six digit numbers. The digits from 0 to 9 were represented on dials; when a one was added to a nine the gear turned to show a zero and the next gear, representing the next higher tens unit, automatically turned. Over 50 of these machines were made. A few remain in existence.

Gottfried Wilhelm Leibniz, a German, created a machine in 1671 which did addition and multiplication. For over 200 years this machine was lost; then it was discovered by some workmen in the attic of one of the Göttingen University's buildings.

Charles Xavier Thomas de Colmar, in 1820, devised a machine which added subtraction and division to a Leibniz type calculator. It was the first mass produced calculator and became a common sight in business offices.