A: The meter is, in essence, a small electrical motor turned by electricity flowing through a voltage coil, which reflects the pressure of electrons moving through the coil, and a current coil to measure the flow of electrons. Multiplying volts by amperes, the measure of current, yields the wattage used. The two coils spin an aluminum disc at a speed proportional to the number of watts being used. The disc is suspended magnetically to reduce friction and provide a sensitive reading. Its rotations are linked to a series of dials by a mechanism similar to that on the odometer of a car. Each rotation of the disc typically measures 7.2 watt-hours, according to Les Rosenau of GE Industrial Systems. Every 138.88 revolutions of the disc measures one kilowatt-hour, the measure used by utilities for billing.