For most of human history, scales used comparison weights; an object was weighed against a counterweight to determine its relative heft. In order to make the calculations consistent, counterweights needed to be uniform and predictable, which is why the ancients relied on grains of wheat or seeds. Seeds from the carob tree gave us the term carats, which we use today to specify the weight of precious gems. A relative weight system can be effective, but it’s also easy to scam. Even so, balance scales became symbols of fairness: Egyptian and Greek goddesses held scales to indicate the quest for justice.
Around 400 B.C. a weighing apparatus called a Bismar appeared, made of a wooden rod slung from a free-moving pivot, with a fixed weight on one end and a hook at the other. Goods were slung from the hook, and the pivot was slid along the rod until the two sides balanced. Greek philosopher Aristotle condemned the device as faulty and unfair, but it remained popular through the next millennium. The European counterweight unit, the stone, dates to antiquity, but a stone’s weight varied wildly until the 14th century, when King Edward III decreed it to be 14 pounds. Leonardo da Vinci came up with plans for a self-indicating scale, but one wasn’t manufactured for centuries.with the accuracy of the candlestick spring scale, which measured tension or pressure to calculate an object’s weight.
Public spring scales began popping up in the streets of Europe, bearing slogans such as, “He who often weighs himself knows himself well. He who knows himself well lives well.” In the 20th century, mechanical scales of all types declined with the development of electronics. Today’s scales are often digital, and some can connect to the Internet and provide highly accurate results—no hooks or stones required.