Curta was a small mechanical calculator introduced in 1947 that supported 11 to 15 digits

The Curta is a small mechanical calculator developed by Curt Herzstark. The Curta’s design is a descendant of Gottfried Leibniz’s Stepped Reckoner and Charles Thomas’ Arithmometer, accumulating values on cogs, which are added or complemented by a stepped drum mechanism. It has an extremely compact design: a small cylinder that fits in the palm of the hand.

The Curta was introduced in 1947, the last models were produced in 1970. It supported 11 to 15 digits making it even more accurate than most simple electronic models today.

Curtas were considered the best portable calculators available until they were displaced by electronic calculators in the 1970s.


The instructions and exercises herein apply both to CURTA model I (8 x 6 x 11 digits) and CURTA model II (11 x 8 x 15 digits). These two models being identical but for their capacity, it has been deemed sufficient to represent only CURTA model I on the illustrations.

View of the CURTA
The basic problem of the design of a mechanical calculator was how to move a gear an amount proportional to the number to be added. The simple stylus/slide adders had an easy answer to this. The user simply placed the stylus in an appropriate hole and the wheel or slide was moved by the appropriate amount. This was undesirable, however, because there was no way for the user to be sure that the correct number had been entered. Also, in the case of multiplications and divisions, the same number would have to be “dialed in” over and over. These problems lead designers to produce more complicated machines.

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