It is the purpose of this Supplement to give instructions and guidance for the accurate determination of electrical power quantities that are commonly needed in support of ASME Performance Test Codes. The choice of method and instruments to be used, required calculations, and corrections to be applied in any given case depend on the requirements of the PTC referencing this Supplement, considering the purpose of the measurement, uncertainty required, and nature of the circuit to be measured. The methods given herein include direct and indirect determinations of active power (watts), reactive power (vars), and power factor produced or consumed in alternating-current single-phase and polyphase electrical circuits, electrical generators, power transformers, and motors. This Supplement does not include such measurements of fundamental electrical properties as voltage, current, frequency, resistance, and impedance, except as needed to support the objectives of this Supplement.