CALCULUS, primarily denotes a little stone or pebble, anciently used in making computations, taking of suffrages, playing at tables, and the like. In after times, pieces of ivory, and counters struck of silver, gold, and other matters, were used in lieu thereof, but still retaining the ancient names. Comptulists were by the lawyers called calculones, when they were either slaves, or newly freed men; those of a better condition were named calculatores or numerarii: ordinarily there was one of these in each family of distinction. The Roman judges anciently gave their opinions by calculi, which were white for abolition, and black for condemnation. Hence calculus albus, in ancient writers, denotes a favourable vote, either in a person to be absolved and acquitted of a charge, or elected to some dignity or post; as calculus niger did the contrary. This usage is said to have been borrowed from the Thracians, who marked their happy or prosperous days by white,
and their unhappy by black, pebbles, put each night Calculus into an urn.
Besides the diversity of colour, there were some calculi also which had figures or characters engraven on them, as those which were in use in taking the suffrages both in the senate and at assemblies of the people. These calculi were made of thin wood, polished and covered over with wax. Their form is still seen in some medals of the Cassian family; and the manner of calling them into the urns, in the medals of the Licinian family. The letters marked upon these calculi were U. R. for uti rogas, and A. for antiquo; the first of which expressed an approbation of the law, the latter a rejection of it. Afterwards the judges who sat in capital causes used calculi marked with the letter A. for absolvo; C. for condemno; and N. L. for non liquet, signifying that a more full information was required.
Calculus is also used in ancient geometric writers for a kind of weight equal to two grains of cicer. Some make it equivalent to the filiqua, which is equal to three grains of barley. Two calculi made the ceratium.