Abacus Abacus, device for performing arithmetic calculations. An abacus is a tablet or frame with grooves or wires on which counters or beads are moved. A modern abacus has a bar across the wires dividing the beads into two groups. Each wire represents one place in the decimal system. The five beads below the crossbar each represent one unit, and the two beads above the crossbar each represent five units.
Beads count when placed against the crossbar.
Many early civilizations used the abacus, and it is still used in China and Japan . The abacus was not invented in China. It originated in Egypt in 2000 BC, almost a millennium before it reached the Orient.