This Technical Report establishes minimum provisions for the surveillance, based on available standards from first commissioning, of devices and systems with measuring function throughout their technical life when used in the activities of the categories listed in the Annex I of the European Directive 2003/87/EC. It does so in order to ensure the compliance with the expected maximum allowable difference of indication. This Technical Report applies to devices/systems with the function to measure: - volumetric or mass amount of natural gas consumption (any type of gas meters), - volumetric amount of natural gas consumption at specified base conditions (conversion devices), - composition of natural gas (gas chromatographs), for calculating, in accordance with the applicable provisions of the guidelines C(2007) 3416, the amount of the CO2 emissions from the source stream of natural gas. Users of this document should be aware that more detailed national recommendations/standards and/or codes of practice as well as national measures possibly approved by National Regulator may exist inside the EU Member States. When national regulations have to be applied, this document should not be considered. Except in the aforementioned case, this Technical Report is intended to be applied in association with applicable national recommendations/standards and/or codes of practice setting out the above mentioned surveillance provisions. In the event of conflict in terms of different requirements in national regulations/standards and in the provisions of this document, the national regulations/standards will take precedence. Referring to the aforesaid Commission's guidelines C(2007) 3416, SFG_I opts for the calculation based method to determine the amount of the CO2 emissions.