Napier's bones

In 1617, the year he died, John Napier, Lord of Merchiston near Edinburgh, published Rabdology, a book in which he described a method of multiplication using a set of small numbered rods. This extremely simple procedure became very popular. These rods, or rulers, bear a number, beneath which are inscribed its multiples. Composing a number by juxtaposing several rods placed next to a fixed rod graduated from 1 to 9 enables the product of this number by any other number – after making, however, some additions – to be read.