ISO 9169:2006 provides definitions and specifies methods to determine performance characteristics of an identified automatic air quality measuring system. Tests are carried out under stable laboratory conditions or field conditions. The automatic measuring system is considered as a black box operated according to specified procedures. ISO 9169:2006 applies to measuring systems for which the following information is available: a description of the automatic measuring system providing the result of measurement in the physical unit of the measurand; operating procedures of the automatic measuring system including, where appropriate, the procedures of routine adjustment, routine verification and calibration; terms of reference for the test program specifying the client requirements and test conditions. ISO 9169:2006 applies to measuring systems for which it is possible to apply several reference materials with accepted values with known uncertainty for the measurand, within the range of application. ISO 9169:2006 does not specify the number of automatic measuring systems to be tested.