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SM-3767 Abacus A simple device useful for counting and among the first calculating devices ever used consists of a wooden board mounted base, over which 'U' shaped brass wires are mounted so that the arms of wires are on each side of the board. Each wire has 20 beads (10 each of two colors), which assists in counting and calculations. A..

SM-3758 Abacus EconomicalSix metallic rods mounted on a wooden base with 30 beads (15 each of black and white) which assists in counting and calculation. SM-3758 Abacus Economical..