M. Vitruvii ... De architectura libri decem, ad Augustum Caesarem accuratiss. conscripti

FROM those things which M. Vitruvius has in the tenth book, and from the monuments of the ancient Greek authors (whom he himself cites), we have taken care to collect the meanings of some characters, as far as it was permitted, and to set them down here separately for your use. I would like you to judge this diligence of ours kindly: we would certainly have provided more, if it had been granted.

I would like you to know that of each named whole—whether a cubit, a foot, a digit, an inch, or an opening—

S. signifies a half.
A symbol representing a quarter a fourth part, not of the named whole, but of the half.
A symbol representing an eighth an eighth part, not of the named whole, but of the half.
u. a duella a small Roman weight/measure, which is the third part of the named whole.
9. A sicilicum a quarter of an ounce/unit, which is the fourth part of the named whole.
z. A drachma a drachma, which is the eighth part of the named whole.
F. The twelfth part of the named whole.
r. The sixteenth part of the named whole.

HOWEVER, since some of the aforementioned characters, and others as well, are found described differently and corrupted in various copies, I do not believe that certain faith should be placed in any single one until you come upon the most corrected example. Indeed, the dots, which are found in that same tenth book either in a circular A circular symbol or square form A square symbol, do not seem to be made for any certain meaning, but only for the sake of distinguishing clauses. Unless perhaps someone were to contend that they signify the minutiae of each whole: if they had been preserved for us as they were handed down, uncorrupted.