662. 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 [z]i.; the drachm, containing three scruples, is marked i.; and the scruple of twenty grains is marked [E]i. The grain weights are marked by little circles, thus:--
+-------+ | o o | Five | o | Grains. | o o | +-------+
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 [E]ss, which means half a scruple; ss, meaning half a drachm, and [z]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.