Troy weight

 Troy Weight

Medicines are made up by troy  weight, although drugs are bought by avoirdupois  weight. There are twelve ounces to the pound troy, which is marked lb .; the ounce, which contains eight drachms, is marked ounce i ; the drachm, containing three scruples, is marked drachm i ; and the scruple of twenty grains is marked scruple i . The grain weights are marked by little circles, thus:
five grains
Each of the grain weights, in addition to the circles denoting their several weights, bears also the stamp of a crown. Care must be taken not to mistake this for one of the numerals. Besides these weights there are others marked scruple ss, which means half a scruple;drachm ss, meaning half a drachm; and ounce ss, meaning half an ounce. When there are ounces, drachms, or scruples, the number of them is shown by Roman figures, thus:—i. ii. iii. iv. v., &c., and prescriptions are written in this style.