The Apothecaries' Weight System
The scale on which a mistake could kill someone.
Origin
Formalised in England by the seventeenth century and given statutory force through successive editions of the London Pharmacopoeia.
The catch
It shares its pound and ounce with troy weight but subdivides them entirely differently. An apothecary weighing to the scruple was working to a precision no grocer needed and no goldsmith used.
The system existed because compounding medicines required ratios that commercial weights could not express safely. Its symbols were a shorthand written on every prescription: the scruple as a stylised script, the drachm as a looped f, and the ounce as the same with a stroke through it. Britain abolished apothecaries’ weights for prescribing in 1971, though the symbols persist in historical pharmacy records and in a good deal of gothic fiction.