The abacus is a computing device on which arithmetic calculations are performed by sliding counters (beads, pebbles, or flat discs) along rods, wires or lines. The instrument may have originated in ...

Blind children are often taught to use the abacus to learn math and perform calculations as a substitute for paper and pencil. In austere field environments, rudimentary abaci have been commonly ...

The Russian abacus (tchoty) is held so that counters move crosswise. It has no crossbar, and all counters in one row have the same value. Most rods have ten counters. An occasional row has fewer, to ...