Whilst most of these early 'pocket calculators' involved a few simple sliding parts, the next major advance was miniaturisation of the more complex mechanical calculators.
Curt Herzstark was an Austrian detained by the Nazis in the Buchenwald concentration camp during World War II. He had been preoccupied with the design of a better calculator for years, having decided to prioritise the user interface: he wanted a device that could be held in one hand and quickly manipulated by the other without a bulky keyboard.
Herzstark revived Leibniz's invention of the single rotating stepped drum, filing his first patent in 1938, and he continued to work on the details of his design whilst imprisoned. His captors encouraged him to work on the device, with the aim of presenting it to Hitler to earn personal glory.
After American troops liberated Buchenwald in 1945, Hertzstark finalised his design and moved to Liechtenstein to manufacture the device, called the Curta calculator (above). The country had little infrastructure to support its manufacture, but the Prince, Franz Joseph II, was so taken with the device that it became the impetus for starting a crown-supported company, Contina.
Because of its complexity - it was composed of over 600 parts - only around 150,000 were ever made. They were widely regarded as the very best portable calculators money could buy until the 1970s, when they were superseded by pocket electronic calculators. One example in the Whipple's collection, a Type I model, was owned by the Cambridge geologist Brian Harland (1917-2003) and used by him during his field trips to the island of Svalbard, Norway.
Curtas are now considered a collector's item, and various websites and groups are devoted to documenting and discussing existing calculators.
