Abacus, bronze calculating table

Calculating table, calculator.

This is a reproduction of a Roman calculator held at the BnF.

It works on the same principles as the abacus, but with some additional complexities.

In addition to the ordinary decimal places, it includes units of measure such as the as (the equivalent of the foot for distances and of the pound for weight) and its fractions.

The as is in base 12, not base 10: one as is worth 12 ounces. It is therefore divisible by 2, 3 and 4, which explains the fraction symbols on the far right:

The names of the multiples of the Roman ounce are taken from monetary vocabulary, the pound corresponding to the as:

1 ounce: uncia
1½ ounces: sescuncia
2 ounces: sextans
3 ounces: quadrans
4 ounces: triens
5 ounces: quincunx
6 ounces: semis
7 ounces: septunx
8 ounces: bes
9 ounces: dodrans
10 ounces: dextans
11 ounces: deunx

For more information, see the excellent paper by Alain Schärlig available here:

https://journals.openedition.org/comptabilites/1491

or the very comprehensive Wikipedia page:

https://fr.wikipedia.org/wiki/Unit%C3%A9s_de_mesure_romaines#:~:text=Les%20noms%20des%20multiples%20de,2%20onces%20%3A%20sextans

It was thus the indispensable tool of the accountant, the agrimensor, the steward, the military officer or anyone holding an administrative or technical management post in the Roman Empire.

This calculator is solid bronze and weighs approximately 240 g.