This Publicly Available Specification specifies the metrological and technical requirements and tests for digital measuring instruments that serve to determine the volume fractions of certain components of the exhaust gases emanating from motor vehicles. The conditions with which such instruments shall comply in order to meet any OIML performance requirements are also established. This Publicly Available Specification is applicable to instruments, particularly those used according to the procedure defined in ISO 3929, intended for the inspection and maintenance of in-use motor vehicles with spark ignition engines. These instruments are used to determine the volume fraction of one or more of the following exhaust gas components: — carbon monoxide (CO), — carbon dioxide (CO2), — hydrocarbons (HC, in terms of n-hexane), and — oxygen (O2) at the moisture level of the sample as analysed. In addition to the measurement of these components, this Publicly Available Specification specifies the lambda calculation for the instruments provided with a facility to determine the value of air/fuel ratio in the exhaust gases. This Publicly Available Specification applies to instruments whose principle of detection is based on infrared absorption in gases for CO, CO2 and HC. Oxygen is generally measured with a fuel cell. This Publicly Available Specification does not exclude any other types of instruments that, although based on other principles of detection, meet the specified metrological and technical requirements and satisfy the associated tests. This Publicly Available Specification defines three accuracy classes of the instruments: Class 00, Class 0 and Class I. This Publicly Available Specification does not apply to equipment for on-board diagnostics incorporated in motor vehicles.