“In the apothecaries’ system of weight units, a pound is divided into 12 ounces, which each consist of 8 drams. A dram is then 3 scruples, each made from 20 grains. I hope that made sense. A grain is one 5,760th of a pound. But not a normal pound: this is a troy pound. Which is different from a normal pound. And people wonder why the metric system was invented.”