Covers the general features concerning tests and calibrations of radon and radon decay product measuring instruments. Emphasizes the definition and use of reference atmospheres. Is intended to help the user or the manufacturer to choose the most appropriate instrument for a given application. Is also intended to help to define type tests which have to be conducted in order to qualify these instruments. See also IEC 61577-2, IEC 61577-3 and IEC 61263.