The Millionaire Calculator, invented in 1892 by Otto Steiger, saved many of the problems associated with other devices’ multiplication. While earlier machines required several turns of their calculating handle to multiply, the Millionaire multiplied a number by a single digit with only one turn of its handle. Its mechanism included a series of brass rods varying in length; these rods executed functions based on the same concept as Napier’s Bones (for more about Napier’s Bones, see above). The calculator was a hit, and around 4,700 machines were manufactured between 1899 and 1935.