Leibniz's "Stepped Reckoner"
"Theoretically this machine could handle the four arithmetic functions, had delayed carrying device, and contained the stepped drum principle, which 150 years later was used in the first commercially successful calculator.

As far as we know, Leibniz built two machines. He spent years of his life improving them so they would be practical. But, the technology of fine instrument making could not yet reach the precision that was essential. Leibniz's dream was unfilled. The story of 18th century calculating devices is one of experiment in which all possible changes were made to the inventions of Pascal, Moreland and Leibniz."

David Weil, Computer Museum of America.

Source: Computer Museum of America.

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