Abacus History

Roman Abacus History

Romans made use of a more advanced design. In Roman abacus several grooves were carved into the board along which counters were moved up and down.One counter was laid in each of the upper grooves, while four in each of the lower grooves. Some additional counters were laid on the right to facilitate the calculation of fractions.

The normal method of calculation in ancient Rome, as in Greece, was by moving counters on a smooth table. Originally pebbles ( calculi ) were used. Later, and in medieval Europe, jetons were manufactured. Marked lines indicated units, fives, tens etc. as in the Roman numeral system. This system of 'counter casting' continued into the late Roman empire and in medieval Europe, and persisted in limited use into the nineteenth century. Due to Pope Sylvester II 's reintroduction of the abacus with very useful modifications,it became widely used in Europe once again during the 11th century This abacus used beads on wires; unlike the traditional Roman counting boards; which meant the abacus could be used that much faster.

Writing in the 1stcentury BC, Horace refers to the wax abacus, a board covered with a thin layer of black wax on which columns and figures were inscribed using a stylus. One example of archaeological evidence of the Roman abacus , shown here in reconstruction, dates to the 1st century AD.

It has eight long grooves containing up to five beads in each and eight shorter grooves having either one or no beads in each. The groove marked I indicates units, X tens, and so on up to millions. The beads in the shorter grooves denote fives –five units, five tens etc., essentially in a bi-quinary coded decimal system, obviously related to the Roman numerals . The short grooves on the right may have been used for marking Roman "ounces" (i.e. fractions).