Promptuary
The promptuary, also known as the card abacus is a calculating machine invented by the 16th-century Scottish mathematician John Napier and described in 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 without the need to write down intermediate results, although some mental addition is still needed to calculate the result. 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. (Wikipedia).
