GJB 8848 is the Chinese national military standard that specifies the test methods used to verify the electromagnetic environmental effects of a complete system. It complements the system level requirements standard by defining how compliance is demonstrated on a platform rather than on a bench, which is a substantially different problem: a system test has to be performed with the equipment installed, with its cables routed as they will be in service and with other systems operating, so the test engineer must contend with an uncontrolled ambient environment, with restricted access to the items of interest and with measurement uncertainty that is difficult to bound. The standard therefore defines the test conditions and the instrumentation, the methods by which the ambient electromagnetic environment is characterised and subtracted, the procedures for measuring emissions from the system and for applying fields and injected currents to it, the transfer function measurements used to relate the results obtained at accessible points to the levels present inside the installation, and the criteria by which the system is judged.