This standard specifies the metrological and technical requirements for the pattern approval and verification of instruments used to determine the mass of liquid contained in a tank using methods which measure mass-related properties of the liquid while it is in a static state, e.g. the hydrostatic pressure of the liquid and gases in the tank. It does not include instruments which determine the mass of the liquid by methods covered by other GSO standard(1) , e.g. by weighing, by measuring the volume and density and converting to mass or by mass flow measurement. This standard also includes pattern approval and verification procedures and test methods. References to other documents are made for construction, installation, operating, requirements and calibration procedures, in particular GSO …./…..(2) Petroleum and liquid Petroleum Products – Direct static measurements – Contents of vertical storage tanks. Part 1: Mass measurement by hydrostatic tank gauging and GSO …./…..(3) Petroleum and liquid petroleum products – Calibration of vertical cylindrical tanks.