The geometric tolerancing defined by standardization is studied in detail according to a structured presentation. This study shows the importance of the concept of compound theoretical surface in functional geometrical specifications such as reference systems or certain types of tolerancing such as the maximum material requirement. These specifications can be verified by traditional methods of marble control and gauge control. The software of the three-dimensional measuring machines (CMMs) does not make it possible to construct, in a manner that complies with the standard, the reference systems on the palpated surfaces of the part, nor to reproduce the controls by caliber. A new approach to metrology is proposed for the software of these machines whose first objective is to overcome these limits. According to this approach the specifications are controlled by the result of the assembly of a "virtual caliber" with the palpated surfaces of the part. This allows direct control of the functional conditions that the part must fulfill. The virtual caliber, defined by the metrologist through the software menus, is a perfect construction of several elementary theoretical surfaces, such as planes or cylinders, which are called "elementary calibres". Different properties can be given to elemental calibres allowing them, for example, to "fit" to palpated surfaces. These properties make it possible to carry out a multitude of controls and functional measurements. A computer model implementing this model has been developed. The use of this model is illustrated on an industrial example and shows the simplicity and effectiveness of the proposed approach
