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. [looks like a z on top of a 3]; the drachm, containing three scruples, is marked [*drachm]i. [looks like a 3]; and the scruple of twenty grains is marked [*scruple]i. [looks like a backwards C with a horizontal cross-bar]. 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 [*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.