47 years ago today: First scientific pocket calculator

On this date in 1972, Hewlett-Packard introduced the world's first scientific pocket calculator. It provided trigonometric and exponential functions. The display used a unique form of multiplexing, illuminating a single LED segment at a time rather than a single LED digit, since HP research had shown that this method was perceived by the human eye as brighter for equivalent power. Light emitting diodes were relatively new at the time and were much dimmer than high efficiency diodes developed in later decades.
The size of this calculator was said to have been designed to fit into one of William Hewlett's shirt pockets.
It was the first scientific calculator to fly in space in 1972.
Over 300,000 HP-35's were sold by the time it was discontinued in 1975.

In 2007, Hewlett Packard introduced a revised HP 35 calculator in memory of the original.
An emulation of the HP-35 is available for the Apple iPhone and iPad.