The arithometer, the first commercially successful mechanical calculator, was invented by Charles Xavier Thomas de Colmar. The Frenchman spent a good three decades working on his apparatus before it saw the light of day in 1851 (remember that year).
Meanwhile, in Poland, Israel Abraham Staffel spent a decade himself working on his own version, completely independent of Colmar. His design was unveiled in 1845, six years before the Frenchman. Staffel's machine could do the four basic arithmetic functions, as well calculate square roots.
Staffel presented his invention to Poland's Russian overlords, who marveled at its capabilities. In 1851, it was demonstrated at the famed Great Exhibition in London's Crystal Palace... together with Colmar's device.
Staffel's invention won first place, but it was Colmar's that entered production. Staffel and his calculator were mostly foregotten.