ISO 4266-3 gives guidance on the accuracy, installation, commissioning, calibration and verification of automatic level gauges (ALGs) both intrusive and non-intrusive, for measuring the level of petroleum and petroleum products having a vapour pressure less than 4 MPa, stored in pressurized storage tanks. ISO 4266-3 gives guidance on the use of ALGs in custody transfer application. ISO 4266-3 is not applicable to the measurement of level in caverns and refrigerated storage tanks with ALG equipment.