Wilhelm Schickard (22 April 1592 – 24 October 1635) was a German professor of Hebrew and Astronomy who became famous in the second part of the 20th century after Dr. Franz Hammer, a biographer of Johannes Kepler, claimed that the drawings of a calculating clock, predating the public release of Pascal's calculator by twenty years, had been discovered in two unknown letters written by Schickard to Johannes Kepler in 1623 and 1624.
Dr. Hammer asserted that because these letters had been lost for three hundred years, Blaise Pascal had been called and celebrated as the inventor of the mechanical calculator in error during all this time.
After careful examination it was found that Schikard's drawings had been published at least once per century starting from 1718, that his machine was not complete and required additional wheels and springs and that it was designed around a single tooth carry mechanism that didn't work properly when used in calculating clocks.
Schickard's machine was the first of five unsuccessful attempts of designing a direct entry calculating clock in the 17th century (including the designs of Tito Burattini, Samuel Morland and René Grillet). Schickard's work had no impact on the development of mechanical calculators.
Schickard was born in Herrenberg and educated at the University of Tübingen, receiving his first degree, B.A. in 1609 and M.A. in 1611. He studied theology and oriental languages at Tübingen until 1613. In 1613 he became a Lutheran minister continuing his work with the church until 1619 when he was appointed professor of Hebrew at the University of Tübingen.
Schickard was a universal scientist and taught biblical languages such as Aramaic as well as Hebrew at Tübingen. In 1631 he was appointed professor of astronomy at the University of Tübingen. His research was broad and included astronomy, mathematics and surveying. He invented many machines such as one for calculating astronomical dates and one for Hebrew grammar. He made significant advances in mapmaking, producing maps that were far more accurate than previously available.
Political theory 
In 1625 Schickard, a Christian Hebraist, published an influential treatise, Mishpat ha-melek, Jus regium Hebraeorum (Title in both Hebrew and Latin: The King's Law) in which he uses the Talmud and rabbinical literature to analyze ancient Hebrew political theory. Schickard argues that the Bible supports monarchy.
Drawings of a calculating clock 
In 1623 and 1624, Schickard drew what he called a Speeding Clock or Calculating Clock on two letters that he wrote to Johannes Kepler and explained that the machine could be used for calculating astronomical tables. The machine could add and subtract six-digit numbers, and indicated an overflow of this capacity by ringing a bell; to add more complex calculations, a set of Napier's bones were mounted on it. Schickard's letters mention that the first machine to be built by a professional, a clockmaker named Johann Pfister, was destroyed in a fire while still incomplete. Schickard abandoned his project soon after.
Incidentally, Kepler used another one of Napier's inventions for his calculations (much more appropriate for computing planets' orbits than his Napier's bones): the logarithm tables; Because of this, Kepler dedicated his Ephemeris to John Napier.
Max Caspar, one of Kepler's biographer, physically found these two letters in 1935 and later. Extrapolating from these findings, Dr. Franz Hammer, another one of Kepler's biographers, challenged in 1957 the fact that Pascal had invented the mechanical calculator by announcing to the world that the drawings of this previously unknown calculating clock, predating Pascal's work by twenty years, had been found in these two letters. Dr. von Freytag Loringhoff, a mathematics professor at the University of Tübingen, built the first replica of this machine in 1960. Dr. Hammer claimed that Blaise Pascal wouldn't have been considered the inventor of the mechanical calculator for three centuries had the world known of Schickard's forgotten machine.
Schickard's drawing had been publicly known since 1718 
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 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 (Retrieved January 31, 2012)
Unfinished design - wrong carry mechanism 
Dr. von Freytag Loringhoff, a mathematics professor at the University of Tübingen built the first replica of Schickard's machine in 1960 but he had to improve on the design of the carry mechanism:
This simple-looking device actually presents a host of problems to anyone attempting to construct an adding machine based on this principle. The major problem is caused by the fact that the single tooth must enter into the teeth of the intermediate wheel, rotate it 36 degrees (one tenth of a revolution), and exit from the teeth, all while only rotating 36 degrees itself. The most elementary solution to this problem consists of the intermediate wheel being, in effect, two different gears, one with long and one with short teeth together with a spring-loaded detente (much like the pointer used on the big wheel of the gambling game generally known as Crown and Anchor) which would allow the gears to stop only in specific locations. It is not known if Schickard used this mechanism, but it certainly works well on the reproductions constructed by von Freytag Loringhoff.—Michael R. Williams, History of Computing Technology, IEEE (1997)
Without this twentieth-century improvement in the carry mechanism, with wheels and springs which are not described in any of Schickard's letters or drawings, the replicas would not have worked. Another problem was found after the replicas were built:
... it is almost certain that Pascal would not have known of Schickard's machine ...
Pascal seems to have realized right from the start that the single-tooth gear, like that used by Schickard, would not do for a general carry mechanism. The single-tooth gear works fine if the carry is only going to be propagated a few places but, if the carry has to be propagated several places along the accumulator, the force needed to operate the machine would be of such magnitude that it would do damage to the delicate gear works.—Michael R. Williams, History of Computing Technology, IEEE (1997)
Schickard's machine used clock wheels which were made stronger, and were therefore heavier, to prevent them from being damaged by the force of an operator input. Each digit used a display wheel, an input wheel and an intermediate wheel. During a carry transfer all these wheels meshed with the wheels of the digit receiving the carry. The cumulative inertia of all these wheels could "...potentially damage the machine if a carry needed to be propagated through the digits, for example like adding 1 to a number like 9,999".
Even though Schickard designed his machine twenty years earlier, Pascal is still the inventor of the mechanical calculator because the drawings of Schickard's calculating clock described a machine that was neither complete nor fully usable.
The Institute for Computer Science at the University of Tübingen is called the Wilhelm-Schickard-Institut für Informatik in his honor.
Notes and references 
- Jean Marguin p. 48 (1994)
- "[...] but it was not until 1642 that Blaise Pascal gave us the first mechanical calculating machine in the sense that the term is used today." Howard Aiken, Proposed automatic calculating machine, presented to IBM in 1937
- "Pascal's invention of the calculating machine, just three hundred years ago, was made while he was a youth of nineteen. He was spurred to it by seeing the burden of arithmetical labor involved in his father's official work as supervisor of taxes at Rouen. He conceived the idea of doing the work mechanically, and developed a design appropriate for this purpose ; showing herein the same combination of pure science and mechanical genius that characterized his whole life. But it was one thing to conceive and design the machine, and another to get it made and put into use. Here were needed those practical gifts that he displayed later in his inventions..." Magazine Nature, Prof. S. Chapman, Pascal tercentenary celebration, London, (1942)
- History of computers The calculating Clock of Wilhelm Schickard. Retrieved January 31, 2012
- Michael Williams, p.122 (1997)
- Michael Williams, p.124,128 (1997)
- Single tooth carry mechanisms worked well in pedometers of the 16th century and were still used in mechanical odometers and gas meters during the 20th century.
- Please see Mechanical calculator#Calculating clocks: unsuccessful mechanical calculators
- René Taton, p. 81 (1969)
- History of Computing Foundation. "Wilhelm Schickard entry at The History of Computing Project". Retrieved 2007-07-19.
- Eric M. Nelson, "Talmudical Commonwealthsmen and the Rise of Republican Exclusivism, The Historical Journal, 50, 4 (2007), p. 826
- Eric M. Nelson, "Talmudical Commonwealthsmen and the Rise of Republican Exclusivism, The Historical Journal, 50, 4 (2007), p. 827
- Lynne Gladstone-Millar; p. 44 (2003)
- Eric Swedin, p.11 (2005)
- Prof. S. Chapman (October 31, 1942). "Blaise Pascal (1623-1662) Tercentenary of the calculating machine". Nature (London) 150: 508–509.
- Williams, Michael R. (1997). History of Computing Technology. Los Alamitos, California: IEEE Computer Society. ISBN 0-8186-7739-2.
- Marguin, Jean (1994). Histoire des instruments et machines à calculer, trois siècles de mécanique pensante 1642-1942 (in fr). Hermann. ISBN 978-2-7056-6166-3.
- Ginsburg, Jekuthiel (2003). Scripta Mathematica (Septembre 1932-Juin 1933). Kessinger Publishing, LLC. ISBN 978-0-7661-3835-3.
- Gladstone-Millar, Lynne (2003). John Napier: Logarithm John. National Museums Of Scotland. ISBN 978-1-901663-70-9.
- Swedin, Eric G.; Ferro, David L. (2005). Computers: The Life Story of a Technology. Greenwood. ISBN 978-0-313-33149-7.
- Taton, René (1969). Histoire du calcul. Que sais-je ? n° 198 (in fr). Presses universitaires de France.
- O'Connor, John J.; Robertson, Edmund F., "Wilhelm Schickard", MacTutor History of Mathematics archive, University of St Andrews.