Justervesenet needs a standard for calibration of gas flow meters. The calibration system will be used with gases such as hydrogen, natural gas, methane, various hydrogen-methane mixtures, and nitrogen. The system must be operating with a pressure range of at least 0 - 60 barg and with flowrates of at least 1 - 100 Sm3/h. A design could be a primary standard based on the measurements of pressure, volume, temperature, and time – pVTt. An example of a pVTt system design is included in Annex 2+3 , collected volumes will be typically up to 850 litres. Justervesenet is open to other primary or secondary standard designs.