Arithmometer

Thomas de Colmar's Arithmometer, first produced in 1820, is where the calculator became a product rather than a curiosity. Inside, it borrowed Leibniz's stepped drums; outside, it was built to be made in numbers, the first calculator to take advantage of industrial manufacturing. Early models were driven by pulling a silk ribbon, later ones by turning a crank, and the operator set digits with sliders before cranking to add, or cranking repeatedly to multiply. Nearly 2,000 were sold and it stayed in production into the 20th century. If the Pascaline proved a machine could add, this proved people would pay for one that kept working.