I do not believe that glassfuls, and so on, are measures of capacity at all.
The capacity should not be in portions or glassfuls, but some measure that everyone recognises.
I will certainly look into the question of glassfuls, "toothfuls"and"skinfuls", and see whether they can be eliminated.
A third of a pint is roughly about a glassful of milk.
I think he was a little apprehensive about the way that such colloquial terms as "skinfuls"and"glassfuls" might be taken.
A glassful may be an indication of the capacity, but it is not a measure of the capacity, and as such would not satisfy paragraph 4.
I had never seen anything like those large glassfuls before.