This part of IEC 61577 describes the specific requirements for instruments measuring the activity concentration of airborne 222Rn and 220Rn outdoors, in dwellings, and in workplaces including underground mines. This standard applies practically to all types of electronic measuring instruments that are based on either spot or continuous measurements. The activity concentration can be measured by pumping or by diffusing the air containing 222Rn and/or 220Rn into the sensitive volume of the detection unit or at a particular moment by taking an air sample (grab sampling).