Wooden tablet featuring series of pebbles, which was used for performing complex mathematical operations. Abacus was a wooden tablet with small pebbles used to calculate complex mathematical operations. Such an abacus, based on the acrophonic (Herodian) numeral system (e.g. Δ to represent Δέκα (ten), Η to represent Ηεκατό (a hundrend), etc.), made of marble and dated from the 4th century B.C., was discovered in 1846 on the island of Salamis and is kept at the Epigraphical Museum of Athens.
One or two sets of parallel lines equally divided by a vertical line are engraved on the board. The parallel lines are used to group the numbers by powers of ten. The space between the lines is used to represent half the value of the line above it. The vertical line is used to divide numbers into positive (right side) and negative (left side). Each number is represented with maximum economy as a combined sum of positive and negative pebbles on the board.
Arithmetic operations were carried out by the combined movement of the pebbles.