The motive force, the capacity to do the work behind the operation of just about anything and everything is energy. Energy is essential for most activities of modern society. Energy can be measured; that is, the amount of energy a thing has can be given a number. As for other kinds of measurements, there are measurement units. The units of measurement for measuring energy are used to make the numbers understandable and meaningful. Most users of the Equivalencies Calculator who seek equivalencies for electricity-related emissions want to know equivalencies for emissions reductions due to energy efficiency or renewable energy programs. Annual energy consumed by a light bulb is calculated by multiplying the power by the average daily use by the number of days per year. The use of steam to power turbines to convert energy is accomplished by machines called heat engines.