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The Curta was invented by Curt Herzstark while he was a prisoner in the Buchenwald concentration camp. Hersztark survived the camp, and after WWII ended he completed and perfected the design. Contina Ltd. produced the devices. They were widely considered the best portable calculators available, until they were displaced by electronic calculators in the 1970s.
Numbers were entered using slides (one slide per digit) on the side of the device. The revolution counter and result counter appeared on the top. A single turn of the crank would add the input number to the result counter, at any position, and increment the revolution counter accordingly. Pulling the crank out slightly before turning it would perform a subtraction instead of an addition. Multiplication, division, and other functions required a series of crank operations. The Type I Curta had 8 digits of slides, a 6-digit revolution counter, and a 11-digit result counter. The larger Type II Curta, introduced in 1954, had 11 digits of slides, an 8-digit revolution counter, and a 15-digit result counter.