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.