Abstract: A calibration process for a pneumatic-assistance servomotor in a braking circuit of a motor vehicle. The values of the output pressure (Pmc) of a hydraulic master cylinder associated with the servomotor and of the negative pressure inside the working chamber of the servomotor are measured and recorded with respect to a given negative-pressure value (Pfc) inside a negative-pressure chamber of a servomotor for several operating points P1, P2, P3, P4 of the servomtotor. The operating points being located on either side of a saturation point to precisely determine the coordinates of the saturation point and thereby provide an accurate control of advanced functions of the servomotor with respect to braking operation, the braking assistance and/or the monitoring of the performance or of the ageing of the servomotor.