Definition:Apothecaries' Weights and Measures/Mass/Ounce/Historical Note

Historical Note on Apothecaries' Ounce
The apothecaries' pound derived from the uncia (Roman ounce).

It is seen that an apothecaries' ounce is the same size as a troy ounce, while weighing approximately $1 \cdotp 1$ ounces avoirdupois.

Some sources do not recognise the existence of the apothecaries' ounce separately from the troy ounce, and when tabulating the various conversion factors refer merely to the fact that $8$ drachms make $1$ troy ounce.