Means for measuring the relative length of a tool mounted on a mocn and of the calibration of the machine, that - ci: - a mandrel carrying - part (13) coupled to a drive means and supported in rotation by bearings, - a spindle carries - tool (14) provided with a tool (10) whose length is to be able to be driven by two means for entrainment in translation along at least two axes perpendicular to one another, this measuring means and of the calibration is characterized by two bearing zones associated with the mandrel and fixed with respect to the latter, the two bearing zones being separated from one another and being secant to two geometrical planes to a geometric axis (o) coincides with the axis of rotation of the mandrel and angularly spaced apart from one another, and that said measuring means comprise: - a unit for processing the information, capable of performing operations of mathematical calculations and provided with a memory block, - a coder linked kinematically to the motor means connected electrically to the processing unit of the information and able to detect the movement of rotation of the mandrel under the effect of a contact of the free end of the tool on a bearing zone, this rotation being characteristic of this contact, and to deliver a signal to the processing unit of the information when this movement of rotation is detected,Moyen de mesure de la longueur relative d'un outil monté sur une MOCN et d'étalonnage de ladite machine, celle-ci comprenant : - un mandrin porte-pièce (13) accouplé à un moyen moteur et porté en rotation par des paliers, - une broche porte-outil (14) dotée d'un outil (10) dont la longueur est à mesurer, apte à être entraînée par deux moyens d'entraînements en translation selon au moins deux axes perpendiculaires l'un à l'autre, ce moyen de mesure et d'étalonnage étant caractérisé par deux zones d'appui associées au mandrin et fixes par rapport à ce dernier, les deux zones d'appui étant écartées l'une de l'autre et étant sécan
