Abacus

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Abacus

The precursor of the pocket calculator is still sometimes found built in to playpens. It is a frame with wires across it, each threaded with 10 beads. It is at least as old as the ancient Greeks (the word is Greek for cyphering table, since it can also be used to teach writing), and it was modified by the Chinese. Rather crude examples from British schools and nurseries are common enough, but elaborate ones were made by the 1600's mathematical instrument maker Robert Jole.