Roman abacus

The Romans developed the so-called Roman abacus, or rather a portable counting board, based on previous Greek counting boards. It was the first portable calculating device for engineers, merchants and presumably tax collectors. It greatly reduced the time needed to perform the basic operations of Roman arithmetic using Roman numerals.

Layout

The Late Roman counting board shown here as a reconstruction contains seven longer and seven shorter grooves used for whole number counting, the former having up to four beads in each, and the latter having just one. The rightmost two groves were for fractional counting. The counting board was made of a metal plate where the beads ran in slots. The size was such that it could fit in a modern shirt pocket.

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