There are various types of tariffs that electric companies use to charge customers for electrical energy. The main tariff types are simple tariff, flat rate tariff, block rate tariff, two-part tariff, maximum demand tariff, power factor tariff, and three-part tariff. Each tariff type determines the rate charged per unit of electricity in different ways, such as having a constant rate, different rates for customer classes, or splitting the total charge into multiple components including fixed demand charges and energy usage charges. Tariffs can also differ based on whether a customer receives low tension or high tension supply, and some utilities implement time of day tariffs where rates vary depending on the time electricity is used.