"[It] computes the given numbers automatically; adds, subtracts, multiplies, and divides."
Wilhelm Schickard
Early inventions to speed up calculations focused on manual solutions such as Napier's bones, which consisted of multiplication tables inscribed onto bones for calculating sums. Seeing John Napier's work, the German polymath Wilhelm Schickard (1592-1635) created a mechanical calculator that automated the process of calculation and incorporated Napier's bones. In 1623, he designed and built the "calculating clock." At around the size of a typewriter, it could handle numbers of up to six digits in length.
The calculator used a direct gear drive and rotating wheels to add and subtract. When a wheel made a complete turn, the wheel adjacent rotated one-tenth of a turn. Dials on the lower part of the machine were turned one way to perform addition, and the opposite way to perform subtraction. These dials were joined by teeth-bearing internal wheels that carried one digit every time the wheel passed from nine to zero. The upper part of the machine used Napier's bones to multiply and divide. The machine was fitted with a bell that rang when a calculation produced a result of more than six digits (and was thus too long to display).
Schickard began building a replica of his calculating clock for astronomer Johannes Kepler but it was never completed because a fire engulfed his workshop. He gave Kepler detailed instructions on how to build the calculator, but then Schickard and his family died of the plague in the 1630s and the prototype was lost. It was not until the 1950s that a sketch of the calculating clock was discovered among Kepler's papers in Russia, proving that Schickard was the originator of the mechanical calculator.
