Justervesenet needs a standard that will enable the calibration of gas flow meters in hydrogen refuelling stations (HRSs). The entire standard is termed HDFTS (Heavy-Duty Field Test Standard). It is a mobile standard that can be lifted onto a car trailer and driven to a HRS for testing. The standard consists of two parts: (1) a pair of Coriolis flow metres operating in parallel and (2) a tank system. Part 1 is termed CMU (Coriolis Measurement Unit) and 2 is HST (Hydrogen Storage Tanks). The operating pressure range must be at least from 0 to 900 barg and the rig must be designed to measure flow rates at least from 0.075 to 18 kg/min at ambient temperatures (15-25°C).