CISPR 16-4-2:2011 is a basic EMC publication. It specifies the method of applying Measurement Instrumentation Uncertainty (MIU) when determining compliance with CISPR disturbance limits. The material is also relevant to any EMC test when interpretation of the results and conclusions reached will be impacted by the uncertainty of the measurement instrumentation used during testing. This second edition includes significant technical additions about methods of conducted disturbance measurements on mains and communication ports and about methods of radiated disturbance measurements using a FAR in the ranges of 30 MHz to 1 000 MHz and of 1 GHz to 18 GHz. The annexes contain the background material used in providing the amount of MIU found in generating the CISPR values shown in the main document and hence provide valuable background material for those needing both initial and further information on MIU and how to take individual uncertainties in the measurement chain into account. The annexes, however, are not intended to be a tutorial or user manual or to be copied when making uncertainty calculations. For that purpose, the references shown in the bibliography, or other widely recognized documents, may be used. Measurement instrumentation specifications are given in the CISPR 16-1 series, while the methods of measurement are covered in the CISPR 16-2 series. Further information and background on CISPR and radio disturbances is given in CISPR 16-3. The other parts of the CISPR 16-4 series contain further information on uncertainties in general, statistics and limit modelling.