Schickard’s “Calculating Clock” is composed of a multiplying device, a mechanism for recording intermediate results, and a 6-digit decimal adding device. Interesting Fact: The letters Schickard wrote ...

The “calculating clock” was developed by German astronomer Wilhelm Schickard and first described in detail to his colleague Johannes Kepler in a 1623 letter.

Calculating machines, which hardly resemble today’s calculators, weren’t invented until the 17th century. ... In 1623, Wilhelm Schickard first conceived of a calculating clock, ...