Balance is a device that weighs substances. The simplest analytical balance consists of a horizontal bar balanced on a thin edge of metal or some other hard substance. A pan is suspended on each end of the bar. A pointer, attached to the bar, swings across a scale as the bar moves up and down. Weights are placed in one pan, and the substance to be weighed in the other. When the weight in both pans corresponds, the arm remains horizontal, and the pointer motionless. This kind of balance can weigh small objects to the nearest 0.1 milligram (4/1,000,000 ounce).