Robin Carroll-Mann recently reported on the SCA-cooks Yahoo list that the following sources on medieval weights and measures are available, in their entirety, on Google Books:
"Italian weights and measures from the Middle Ages to the nineteenth
century" By Ronald Edward Zupko
"A dictionary of weights and measures for the British Isles: the
Middle Ages ..." By Ronald Edward Zupko
The URLs link to the Google Book location of each. I am reporting these by way of expanding access to this source of information.
EDIT: Note the comment by heroquester below. Zupko may be useful but may not be completely trustworthy.