Equal-Arm Balance on a Knife Edge, with a Set of Brass Weights

The oldest weighing machine is a beam with equal arms balanced on a pivot, a pan hanging from each end: put the load in one pan and known weights in the other until the beam lies level. Balances go back to the Fourth Dynasty of Egypt. A hardened knife edge makes it sensitive and a long pointer shows the smallest tilt; the weights are cast in brass and adjusted against each other. The picture: our diagram of the balance, its knife edge, pointer, pans and weights.