~1680: Liebniz works out binary arithmetic (2, p17)

1. John J. O'Conner and Edmund F. Robertson, "Gottfried Leibniz," http://turnbull.dcs.st-and.ac.uk/history/Mathematicians/Leibniz.html (School of Mathematics and Statistics, University of St. Andrews, Scotland, accessed 2003 Sep 13).

2. Paul E. Ceruzzi, Reckoners, the Prehistory of the Digital Computer, from Relays to the Stored Program Concept, 1935-1945 (Westport, CT: Greenwood Press, 1983). Also available online at http://www.computerhistory.org/collections/DocumentArchive/Documents/Books/Reckoners/Reckoners.html (Computer History Museum, accessed 2003 Sep 27).