Gives a designation and a defination to each instrument considered. As an exception, in the field of control and safety of nuclear reactors, this recommendation also defines certain apparatus which do not belong to the category of electrical measuring instruments in view of the necessity of considering nuclear reactor instrumentation as a whole. Instruments are grouped into the following sections: apparatus - equipment - assembly - sub-assembly - basic function unit, (radiation) measuring assembly - (radiation) monitor - (radiation) indicator, basic radiation measuring apparatus, special apparatus for the control and the safety of nuclear reactors, special apparatus for health physics, special apparatus for the prospection and for the mining industry, apparatus using, for the measurement, an ionizing radiation source.