 Leibniz is known for both the development of formal techniques in philosophy and the design and production of actual computational machinery. In 1642, the philosopher Blaise Pascal had invented the Pascaline, designed to add with carry and subtract. Between 1673 and 1720 Leibniz designed a series of calculating machines intended to instantiate multiplication and division as well: the stepped reckoner, employing what is still known as the Leibniz wheel (Martin 1925). The sole surviving Leibniz step reckoner was discovered in 1879 as workmen were fixing a leaking roof at the University of Göttingen. In correspondence, Leibniz alluded to a cryptographic encoder and decoder using the same mechanical principles. On the basis of those descriptions, Nicholas Rescher has produced a working conjectural reconstruction (Rescher 2012).