<P> A mechanical calculator, or calculating machine, was a mechanical device used to perform automatically the basic operations of arithmetic . Most mechanical calculators were comparable in size to small desktop computers and have been rendered obsolete by the advent of the electronic calculator . </P> <P> Surviving notes from Wilhelm Schickard in 1623 reveal that he designed and had built the earliest of the modern attempts at mechanizing calculation . His machine was composed of two sets of technologies: first an abacus made of Napier's bones, to simplify multiplications and divisions first described six years earlier in 1617, and for the mechanical part, it had a dialed pedometer to perform additions and subtractions . A study of the surviving notes shows a machine that would have jammed after a few entries on the same dial, and that it could be damaged if a carry had to be propagated over a few digits (like adding 1 to 999). Schickard abandoned his project in 1624 and never mentioned it again until his death eleven years later in 1635 . </P> <P> Two decades after Schickard's supposedly failed attempt, in 1642, Blaise Pascal decisively solved these particular problems with his invention of the mechanical calculator . Co-opted into his father's labour as tax collector in Rouen, Pascal designed the calculator to help in the large amount of tedious arithmetic required.; it was called Pascal's Calculator or Pascaline . </P>

Who built the first gear-driven mechanical calculator that did addition and subtraction