This chapter deals with the use of standard and specialized test equipment and perhaps most importantly with common sources of error in their use. It describes the use of commonly available or easily manufactured and relatively inexpensive equipment that may be used for simple diagnostic measurements as well as the use of specialized equipment. Diagnostic measurements are used to locate the source of emissions and the area of susceptibility. In addition, measurements on circuits and equipment may be used in an electromagnetic compatibility (EMC) prediction to provide the magnitude of fields, voltages, or currents on which an analysis is based. Basic standards define and describe the EMC problem, measurement and test methods, principle measuring instruments, and test setup. Commercial requirements are typically confined to limits on conducted and radiated emissions. The control of emission on EDP equipment in Japan is undertaken on a voluntary basis under the supervision of the Voluntary Control Council for Interference.