What is a watt-hour meter?

  A watt-hour meter is a device which measures and registers electric power usage during a period of time. This meter should not be confused with a wattmeter, an in­strument that measures the amount of electric power at any instant.
  The most common watt-hour meter is the familiar glass-enclosed device attached to most houses. This meter, called an induction-type watt-hour meter, has the same basic parts as other specialized watt-hour meters; the difference is the method of applying electricity through the meter circuit. The parts are: stator, rotor, retarding magnets, register, and meter housing.
  Induction-type meters measure alternating current electricity. Incoming electricity, passed through the stator, causes the rotor to revolve, as in the operation of an electric motor. Windings (wire) in the stator relate the particular combination of voltage and current to the speed of rotation. The retarding magnets control the rotor speed to keep it proportional to the power. The more watts consumed, the faster the rotor turns.
  Through a gear train the rotor turns four dials in the register. The dials indícate how many kilowatt hours (1000 watt-hours) have been consumed. By reading the meter, and subtracting from that reading the previous measurement, the electric company can determine how much electricity has been used.