In shops, merchants used the pan balance to weigh out goods for customers. It had two pans hung from a centrally-balanced arm; the merchant owned a set of iron or brass weights to set on the empty pan until the two balanced. The size of the balance and its pans depended on the type of things the merchant sold.
Goldsmiths and apothecaries used very tiny, precise balances. Spices, the medieval raw materials of medicine, had to be weighed in small and very precise amounts using ounces and drams. There were at least two different measurement systems for spices; the alternative to the royal system was the “Troy weight” system. It was developed in the huge fair at Troyes, in Champagne. The Troy system counted 12, not 16, ounces in a pound.
Goldsmiths’ scales had to be most accurate of all because they could check the value of coins. (“Goldsmith” included those who worked in silver, too.) Their balances were themselves products of careful goldsmith work, except for some rare fine balances carved from ivory. Gold was measured out in grains; the first weight used to counter-balance a “grain” of gold was the seed (grain) of a carob plant. The carob seed (not an accurate measure!) led to the standardized “carat” measurement of traditional gold work.
On the other side of the size scale, wholesale goods were weighed using a steelyard balance. The Hanseatic League, Europe’s first cartel, controlled the sale of salt, which came in huge amounts. So the League developed a standardized large balance, based on a concept that had been in use since Roman times. The League’s port in London was nicknamed “Steelyard,” which lent its name to the style of balance.
The steelyard balance does not use pans set at equal distances from the fulcrum. Instead, the fulcrum is very close to one end, the end that has a hook for weighed goods to hang. Since the remaining arm is so much longer, it acts as a lever to weigh objects that are actually much heavier than the available iron weights. The doctors’ scales that we all grew up with (before digital) worked on this principle. The beam where the weights hang is calibrated to tell its operators how much to multiply the hanging weights in order to know the object’s true weight, based on how far the weights are from the fulcrum. (Which is why those dinky little metal slides could balance against our bodies.)
The Port of London had its own regulatory team to oversee everything unloaded from ships. Customs officials employed men and horses to roll or carry casks, sacks, and crates to weighing stations. The Port oversaw dividing these goods among the waiting local merchants. Measuring teams worked on grain, salt, and other things separately. After the importing ship paid its customs dues, the local merchants paid each measuring team for its services.
next: measuring dry volume and length