In 1972 the Hewlett Packard Corporation placed on the market the revolutionary HP-35 pocket scientific calculator which utilised integrated circuitry and provided output on a red LED screen. This calculator held a stack of memories to which, using the reverse polish notation method, operations could then be sequentially applied. Operations included not only addition, subtraction, multiplication and division, but a wide slate of trigonometic and other functions, including logarithms and the operations which could be utilised with them. It was a game changer and effectively brought the utility of all prior calculating machines to an end. This collection currently holds an HP-35 and an HP-45 calculator. Notes * The HP-45 in this collection was kindly donated by John Dean. References *[[http://en.wikipedia.org/wiki/HP-35 | Wikipedia article on the HP-35]] *[[http://www.hpmuseum.org/ | The museum of Hewlett Packard Calculators]] *[[http://www.lkjsdf.com/archive/hp/35/manual/| HP-35 Operating Manual]]