METERS, measure the total energy used in electric circuits (f ecdt). The Board of Trade unit of electrical energy is the kilowatt hour (amperes x volts X hours 1,000) . The energy taken from D.C. circuits at constant voltage can be measured by ampere-hour meters which may be of the electrolytic or dynamometer type; but in A.C. circuits the power factor has
to be allowed for, and dynamometer or induction wattmeters provided with a time integrating device must be employed. (See