For many years, the term power, in association with electricity, has tended to lose its true meaning; so, power is often found used in nontechnical literature where actually the correct term energy should be used.

By definition, power is the rate at which energy is transformed or is made available and is measured in watthours.

From an economic viewpoint, the most important of all electrical measurements is the measurement of energy. The watthour meter in various forms can be found in nearly every home, factory, highway billboard, and other locations where electrical energy is being purchased.

Metering, installation and wiring have been governed by national, industrial, and local codes for so many years that, at least in the United States, a particular type of installation is nearly identical everywhere in the country.

Measurement of energy is almost always with a "fixed-installation metering". This provides safety because of the grounding of the meter enclosure and ease of reading as a result of a proper location and mounting.

Tamper-proof housing, which are also weatherproof where necessary, are typical structures that normally insure the integrity of the electric meter readings.