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The promptuary was a calculating machine invented by the 16th-century Scottish mathematician John Napier and described in the second edition of his book Rabdologiae in which he also described Napier's bones.

It is an extension of Napier's Bones, using two sets of rods to achieve multi-digit multiplication. The rods for the multiplicand are similar to Napier's Bones, with repetitions of the values. The set of rods for the multiplier are shutters or masks for each digit placed over the multiplicand rods. The results are then tallied from the digits showing as with other lattice multiplication methods.

The final form described by Napier took advantage of symmetries to compact the rods, and used the materials of the day to hold system of metal plates, placed inside a wooden frame.[1]


  1. ^ Bradley, Michael John (2006), The Age of Genius: 1300 to 1800, Infobase Publishing, p. 36, ISBN 978-0-8160-5424-4 .

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