Caption:
Chinese abacus counting frame, a calculating tool that was in use in Europe, China and Russia, centuries before the adoption of the written Hindu-Arabic numeral system. The exact origin of the abacus is still unknown. Today, abacuses are often constructed as a bamboo frame with beads sliding on wires, but originally they were beans or stones moved in grooves in sand or on tablets of wood, stone, or metal.. Abacuses come in different designs