Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
As a basis for the notion of a whole made up of equal parts, nothing so readily suggests itself as the hand with its five, or the hands with their ten, fingers; upon this rests the decimal system. We have already observed that these elements of all numeration and measuring reach back not merely beyond the separation of the Greek and Latin stocks, but even to the most remote primeval times.
The antiquity in particular of the measurement of time by the moon is demonstrated by language;(1) even the mode of reckoning the days that elapse between the several phases of the moon, not forward from the phase on which it had entered last, but backward from that which was next to be expected, is at least older than the separation of the Greeks and Latins.
1. Cf. I. II. Indo-Germanic Culture
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/1-14-measuring-writing.asp?pg=2