HP-35

The HP-35 was the world's first pocket electronic scientific calculator.

It was introduced in January 1972 by Hewlett-Packard and had the equivalent of 30,000 transistors. It sold for $395.

Hewlett-Packard sold over 100,000 of the HP-35s the first year.

The introduction of the HP-35 and other electronic calculators that followed marked the end of the mechanical slide-rule as a primary problem solving device.