Wilhelm Schickard (Herrenberg, 1592 – Tübingen, 1635), mathematician and astronomer at the University of Tübingen, designs in 1623 the first documented mechanical calculator in history. The device automatically adds and subtracts up to six digits using toothed wheels with a carry mechanism, and aids multiplication via cylinders based on Napier's rods. Schickard describes the machine in two letters to Johannes Kepler (1623 and 1624, preserved in the Pulkovo archives), asking him to have one built for his astronomical calculations. The original prototype was destroyed in a fire during the Thirty Years' War. It was reconstructed in 1960 by Bruno von Freytag Löringhoff. The canonical narrative credits Pascal (1642), ignoring Schickard for 19 years.