Ab'acus, a calculating machine used in teaching the elements of number. It consists of a rectangular frame which holds parallel rods upon which beads or balls are strung. A handle is attached to the lower side of the frame, so that when the abacus is in use the rods are held in a horizontal position. The ancient abacus contained vertical columns which corresponded to the order of figures, as units, tens and hundreds. This instrument was in general use among the Greeks and Romans, and is still employed in Persia and other countries of the Far East for reckoning purposes. The Chinese abacus is called shwanpan, which means reckoning board.