## The Steelyard

The steelyard is a balance used for measuring weights. It has been used since Roman times, and is especially useful where portability is required, or where the weight to be measured can be suspended from a hook – bags of gold or rice for example.

The weight to be measured is hung from a hook or put in a pan (top left), and a sliding weight moved until the steelyard balances horizontally. Taking moments abount the balance point A gives

In fact the scale above right is calibrated so the weight can be read directly in appropriate units. If a pan is used, the weight of this must be subtracted. Some modern weighing scales use the same principle.