Definition:Roman Weights and Measures/Mass/Calcus/Linguistic Note

Linguistic Note on Calcus

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.