772 by 396. The multiplication process required only addition, and no intermediate results needed to be written down. An Example of the Promptuary in the National Archaeological Museum of Spain An example of the Promptuary is in the National Archaeological Museum of Spain in Madrid. It also includes an example of Napier's bones. The apparatus is a box of wood with inlays of bone. In the top section it contains the "bones" calculation device, and in the bottom section is the promptuary. This example consists of 300 stored cards in 30 drawers. One hundred of these cards are covered with numbers (referred to as the number cards). The remaining two hundred cards contain small triangular holes, which, when laid on top of the number cards, allow the user to see only certain numbers. By the capable positioning of these cards, multiplications can be made up to the limit of a number 10 digits in length, by another number 20 digits in length. In addition, the doors of the box contain the first powers of the digits, the coefficients of the terms of the first powers of the binomial and the numeric data of the regular polyhedra. It is not known who was the maker of this piece, nor if it is of Spanish origin or came from a foreigner, although it is probable that it originally belonged to the Spanish Academy of Mathematics (which was created by Philip II) or was a gift from the Prince of Wales. The only thing that is sure is that it was conserved in the Palace, whence it was passed to the National library and later to the National Archaeological Museum, where it is still conserved. In 1876, the Spanish government sent the apparatus to the exhibition of scientific instruments in Kensington, where it received so much attention that several societies consulted the Spanish representation about the origin and use of the apparatus. References External links How to Use the Promptuary Rods for Multiplication and Division Mechanical calculators Scottish inventions Multiplication