Abacus

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Abacus

An instrument allowing one to quickly add and subtract numbers. Generally, an abacus is composed of a rectangular frame in which horizontal rods are partially covered with beads. The beads may be moved one way or the other to make calculations. It was invented in China in the 2nd century CE and is considered the earliest calculator.
References in periodicals archive ?
Have your students clear their abacuses by sliding the beads in heaven to the top and the beads in earth to the bottom.
Next have your students clear their abacuses and enter 10 on the rods by sliding one bead on the tens rod up to the crossbar.
Pick numbers for students to enter on their abacuses, give them a moment to make the numbers, then show them the correct bead placement on the overhead projector to allow them to check their answers.