Defines the methods for measurement and interpretation of results for power quality parameters in 50/60 Hz a.c. power supply systems. The power quality parameters considered in this standard are power frequency, magnitude of the supply voltage, flicker, supply voltage dips and swells, voltage interruptions, transient voltages, supply voltage unbalance, voltage and current harmonics and interharmonics, mains signalling on the supply voltage and rapid voltage changes. Depending on the purpose of the measurement, all or a subset of the phenomena on this list may be measured. This standard is a performance specification, not a design specification. The uncertainty tests in the ranges of influence quantities in this standard determine the performance requirements. This standard gives measurement methods but does not set thresholds.