Soroban Japanese abacus, 2001.
© Science Museum / Science & Society Picture Library
A soroban Japanese abacus with 15 rods, made from bamboo and plastic. The soroban is a derivation of the Chinese Suan Pan abacus and is operated in the same way. It differs from the Suan Pan in only having one bead above the cros-bar, and since the 1930s only four beads below. Numbers are set by moving beads up and down to touch the horizontal cros-bar. Taking any particular rod as the unit rod, the rods to the left represent tens, hundreds, thousands, and so on; those to the right being tenths, hundredths, and so on.