The IEC 61577 series covers the general features concerning test and calibration of radon and radon decay product measuring instruments. This standard addresses only the instruments and associated methods for measuring isotopes 220 and 222 of radon and their subsequent short-lived decay products in gases. Its object is to help to define type tests which have to be conducted in order to qualify these instruments. NOTE These type tests will be described in the future IEC 61577-2-1, IEC 61577-2-2, IEC 61577-3-1 and IEC 61577-3-2 (see IEC 61577 structure in Annex A). For the suitability of the document, this standard also proposes a classification of the instruments measuring radon or RnDP based on the duration of sampling.