Power companies loan watthour meters to their customers. These measure the amount of electricity that the customers use. The meter is usually placed outside, near the spot where the wires from the local step-down transformer enter a building. A worker from the power company comes by to read the meter once a month. The last month's reading is subtracted from the new reading to calculate the amount of kilowatt-hours that have been used.
A kilowatt-hour is a one-hour use of 1000 watts. For example, if ten 100 watt light bulbs are left on for one hour, this would equal one kilowatt hour (10 X 100 = 1000). A kilowatt-hour from a power company costs about ten cents. One kilowatt-hour supplied by dry cell batteries would cost hundreds of dollars!
WATTHOUR METER