In 1678 the French watchmaker René Grillet presented his calculating device in the Journal des Sçavans, of which two original versions or fragments have survived and are housed in CNAM, Paris. A further not authenticated version is in the IBM Collection, New York. The replica shown here is a copy of the latter version. A fourth version, of unknown production date, is privately owned in North Germany and was used to build a replica in the Brunswick State Museum. The gadget features seven cylindrical rods in the box, akin to Napier‘s Rods (known since 1617), and three rows of eight numbered discs each in the lid. It is built of wood, cardboard and paper and can be used for all four operations of arithmetic. Multiplication and division are performed with the Napier cylinders (the two leftmost cylinders are for forming squares and square roots), and addition and multiplication are performed by means of the discs in the cover which are moved with a stylus. It features complementary numbers for subtraction. Its capacity goes from “nombre” at the right to “dixaine 3” (ten million) at the left. There is no tens-carry mechanism and for this reason the complementary numbers are not relative to 9 but to 10. The gadget bears the inscription “Grillet Inventeur Orlogé Paris Avec Privilege du Roy“.