The modified Omega method included in ISO/FDIS 4126-10 provides the highest accuracy compared to other modified models frequently used in practice and academia. At the same time, it allows for an exceptionless oversizing of the necessary relief area under all test conditions. Nevertheless, the average or statistical reproductive accuracy is characterized by an unacceptably high logarithmic scatter of about 80 % for fluid dynamic critical steam/water and two-phase refrigerant R-134a flow. When applying the method to sizing situations with predicted mass flow qualities in excess of I % an acceptably modest oversizing is maintained.