It is shown that the design and management of foundry technology due to its multifactoriness, intensity and inaccessibility for measurements is extremely difficult, which means that a significant number of castings in real production are rejected. A method is proposed for using instead of particular parameters the functional that unites them, which is also used as a dimensionless numerical criterion for the defectiveness of casts. The method is tested in real production with a positive technical effect. The work is devoted to improving the quality of steel castings obtained in sand molds. An increase in the efficiency of designing and improving the management of the process of their manufacture through the development and implementation of new metrological support has been achieved. Its purpose is measurement of the functional criterion in the system «steel casting – sand mold». To achieve this aim, an analysis of the parameter-functional «gas removal» in the system «casting – sand mold» is made. The accuracy and reliability of the use of the complex parameter-functional as a criterion of defect-free casting is estimated. The estimation of accuracy and reliability performed by the proposed method shows that the measurement error of the «gas removal» functional under the conditions of steel casting described above in sandy-resin forms does not exceed 8 %. This is quite acceptable for this type of technical applications, and also with a probability of not less than 0.85, reliably guarantees the high quality of the casting surface, both in the absence of sand burning and in the absence of blown holes.