A method, to decompose the total instantaneous power, into active and non-active components, using the voltages and currents at the metering point; and apparatus implementing the said method. The voltage and currents are transformed into Fourier components. The Fourier currents are separated into active and non-active parts. The active and non-active currents together with the corresponding voltage are used to define the instantaneous total, fundamental and five, active and non-active, power components. Definitions of average values for these are also stated. These components, in various combinations, are useful for measurement, compensation, detection of distortion and power quality. The method can be implemented in a signal processor based power meter, analyzer or controller or used in a software based application.