Definition:Roman Weights and Measures/Mass/Calcus

Definition

The calcus is the smallest unit of mass in the Roman system of weights.

$1$ calcus $= \dfrac 1 8$ scrupulus.

Its value in modern units is estimated to be approximately $2.2$ grains, or approximately $0.14$ grams.

Linguistic Note

The word calcus can be found in David Wells: Curious and Interesting Numbers, in his discussion on the number $12$ (twelve).

This has not been corroborated on the Internet, and it is possible that it is a misprint for calculus, which is Latin for small pebble.

Its plural, on the assumption that it is a second declension noun, which is reasonable, would be calci.

Sources

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $12$
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $12$