The difference between one month's reading and the next is the amount of energy units that have been used for that billing period. | Photo courtesy of Warren Gretz, NREL.
The basic unit of measure of electric power is the Watt. One thousand Watts are called a kilowatt. If you use one thousand Watts of power in one hour you have used a kilowatt-hour (kWh). Your electric utility bills you by the kWh.
The standard electric power meter is a clock-like device driven by the electricity moving through it. As the home draws current from the power lines, a set of small gears inside the meter move. The number of revolutions is recorded by the dials that you can see on the face of the meter. The speed of the revolutions depends on the amount of current drawn; the more power consumed at any one instant, the faster the gears will rotate.
When reading an electric meter, read and write down the numbers as shown on the dials from right to left. When the pointer is directly on a number, look at the dial to the right. If it has passed zero, use the next higher number. If the dial has not passed zero, use the lower number. Record the numbers shown by writing down the value of the dial to your extreme right first and the rest as you come to them. Should the hand of a dial fall between two numbers, use the smaller of the two numbers.
Note that some newer electric meters use digital displays instead of dials. The difference between one month's reading and the next is the amount of energy units that have been used for that billing period.
You may also wish to contact your local utility company for more information about reading your electric meter.