Apothecaries’ weight

What is Apothecaries’ weight?

Apothecaries’ weight definition and meaning on Dictionary terms:
noun

a system of weights used chiefly in compounding and dispensing drugs: 20 grains = 1 scruple (?); 3 scruples = 1 dram (dr); 8 drams = 1 ounce); 12 ounces = 1 pound. The grain, ounce, and pound are the same as in troy weight, the grain alone being the same as in avoirdupois weight.