When you drive into a petrol station to fill up your tank, you probably do not think too much about whether the price shown is correct or not; you would just pay it. However, we have been selling petrol for cars for over a century, and through this time have gained expertise and confidence in our ability to accurately meter petrol. Hydrogen refuelling stations however are fairly new and each time a fuel cell vehicle is filled we rely on the flow meter to accurately determine the amount of hydrogen dispensed under challenging conditions; high pressures of 700 bar, fluctuating temperatures, and hydrogen itself is fairly hard to meter. Guidance around accuracy requirements for hydrogen metering and stations (OIML R 139-1) specifies a maximum permissible error of 1% should be provided and in order to achieve this challenging accuracy NMIs need to provide primary standards for flow metering that ensure the flow meters are traceable to the kilogram. As part of the MetroHyVe project METAS has developed a new gravimetric primary standard which was tested at the Empa hydrogen refuelling station in Switzerland. The dispensed hydrogen is collected in two high pressure tanks mounted on a scale, weighed and compared to the amount displayed by the dispenser. The pressure in the tanks can go up to 875 bar. The field test standard also has an ATEX Certification meaning it can be used in explosive atmospheres. This is one of the four standards that will be deployed for field testing at 350 bar and 700 bar during next year.