exist; it was rediscovered at the end of the 19th century, having spent 250 years forgotten in an attic at the University of Göttingen. The German calculating-machine inventor Arthur Burkhardt was asked to attempt to put Leibniz' machine in operating condition. His report was favorable except for the sequence in the carry. and "therefore, especially in the case of multiple carry transfers, the operator had to check the result and manually correct the possible errors". Leibniz had not succeeded in creating a calculator that worked properly, but he had invented the Leibniz wheel, the principle of a two-motion mechanical calculator. He was also the first to have cursors to inscribe the first operand and a movable carriage for results. There were five additional attempts at designing "direct entry" calculating machines in the 17th century (including the designs of Tito Burattini, Samuel Morland and René Grillet). Around 1660 Claude Perrault designed an abaque rhabdologique that is often mistaken for a mechanical calculator because it has a carry mechanism in between the numbers. But it is actually an abacus, since it requires the operator to handle the machine differently when a carry transfer takes place. Pascal's calculator was the most successful mechanical calculator developed in the 17th century for the addition and subtraction of large numbers. The stepped reckoner had a problem in the carry mechanism after more than two consecutive carries, and the other devices had carry mechanisms (one tooth wheel) that were limited in their capacity to carry across multiple digits or had no carry mechanism in between the digits of the accumulator. Calculating machines did not become commercially viable until 1851, when Thomas de Colmar released, after thirty years of development, his simplified arithmometer, the first machine strong enough to be used daily in an office environment. The Arithmometer was designed around Leibniz wheels and initially used Pascal's 9's complement method for subtractions. See also Adding machine Stepped Reckoner Arithmometer Comptometer Difference engine Analytical engine Z1 (computer) Notes Sources External links Website explaining the operation of a Pascaline. Detailed animation explaining how the Pascaline works. More detail on the history of the Pascaline and contemporary replicas. More on the 'operating instructions' for a Pascaline. "Avis nécessaire à ceux qui auront curiosité de voir ladite Machine et s'en servir" (Pascaline, 1635), online text and analysis on BibNum [click 'à télécharger' for English version]. Mechanical calculators Blaise Pascal French inventions