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Abacus
The abacus is a counting device of very ancient origin; evidence of its use has been found in many cultures all over the world, including ancient Greece and Rome and mediaeval Europe. In the 20th century, use of the abacus is restricted to the middle and eastern parts of Central Asia, China and Japan. The modern Japanese abacus (soroban) is a versatile instrument and it can be used to make complex calculations at high speed. The frame is divided longitudinally into two sections, the upper section having one bead per rod representing five digits and the lower section having four beads, each representing one digit. Sets of tables must be learned before multiplication and division can be perfonned on the soroban but with these tables as a basis there is almost unlimited calculation potential. Skilled exponents can visualise the instrument and the progressive movements of the beads, thus carrying out lengthy and complex calculations "in the head", and at great speed. Some Japanese children are remarkably skilled at this.