This part of IEC 61000-4 defines the methods for measurement and interpretation of results for ower quality parameters in 50/60 Hz a.c. power supply systems. easurement methods are described for each relevant type of parameter in terms that will ake it possible to obtain reliable, repeatable and comparable results regardless of the ompliant instrument being used and regardless of its environmental conditions. This standard ddresses measurement methods for in situ measurements. easurement of parameters covered by this standard is limited to those phenomena that can e conducted in a power system. These include the voltage and/or current parameters, as ppropriate. he power quality parameters considered in this standard are power frequency, magnitude of he supply voltage, flicker, supply voltage dips and swells, voltage interruptions, transient oltages, supply voltage unbalance, voltage and current harmonics and interharmonics, mains ignalling on the supply voltage and rapid voltage changes. Depending on the purpose of the easurement, all or a subset of the phenomena on this list may be measured. his standard is a performance specification, not a design specification. The uncertainty tests n the ranges of influence quantities in this standard determine the performance requirements. his standard gives measurement methods but does not set thresholds. he effects of transducers being inserted between the power system and the instrument are cknowledged but not addressed in detail in this standard. Precautions on installing monitors n live circuits are addressed.