History of computers The calculating Clock of Wilhelm Schickard. Consultée le 31 janvier 2012
In 1718 one of the first biographers of Kepler—the german Michael Gottlieb Hansch (1683-1749), published a book of letters of Kepler, which includes the two letters from Schickard to Kepler. There is even a marginal note of the publisher Schickardi machina arithmetica at the second letter, obviously on the calculating machine.
In 1899 in the Stuttgart's surveying magazine Stuttgarter Zeitschrift für Vermessungswesen was published an old article for the topography in Württemberg, Germany, written many years ago and probably published in other editions, by the famous german scientist Johann Gottlieb Friedrich von Bohnenberger (1765–1831). In this article the name of Schickard is mentioned several times, not only concerning his important contribution in the field of topography, but it is mentioned also that ...it is strange, that nobody admitted, that Schickard invented a calculating machine. In 1624 he ordered a copy for Kepler, but it was destroyed in a night fire. Bohnenberger (known mainly as the inventor of the gyroscope effect), just like Schickard, studied and later was appointed a professor of mathematics and astronomy at the University of Tübingen since 1798.
In 1912 in the yearly german magazine Nachrichten des Württembergischen Vermessungstechnischen Vereins was published the sketch and the notes of the machine from the Württembergischen Landesbibliothek. The calculating Clock of Wilhelm Schickard. History-computer.com (Consultée le 31 janvier 2012)
