'Genaille's rods', French, 1885.
© Science Museum / Science & Society Picture Library
A boxed set of 'reglettes multiplicatrices' by Henri Genaille. There was a revival of interest in the calculating device known as Napier's bones in France in the late 19th century when Henri Genaille simplified their use. Instead of having to add the components in a given area, the user simply follows the pointers to multiply or divide. These sets of cards are known as 'Genaille's rods'.