1891 invention that allowed the user to read off the results of simple multiplication or division problems directly, with no intermediate mental calculations.
In the days before calculators, methods of simplifying calculations were of much interest. In 1617 Napier also published a book describing a method to multiply, divide and extract square roots using a set of bars or rods. These became known as Napier's Bones. (avail on our website)
In the late 1800s, Henri Genaille, a French civil engineer, invented an improvement to Napier's Bones that eliminates the need to handle carries from one digit position to the next. The problem was posed by Edouard Lucas and thus the alternate name of Genaille-Lucas Rulers (or Rods) .
Available in either Multiplication or Division.
The process of multiplying any integer of any length by a digit 1-9 is reduced to looking up numbers on the rods. Studying how and why these rods work can provide real insight into the nature of multiplication.
The process of dividing any integer into a number of any length is reduced to looking up numbers on the rods. Studying how and why these rods work gives real insight into the nature of division.