The present invention relates to an optical measurement apparatus, comprising a reference support unit (40) equipped with a fixed headstock (57) and a movable tailstock (60) opposed to the fixed headstock (57) and movable along a linear axis (X) in order to be close to or depart from the headstock (57) and to maintain a piece to be measured between headstock and tailstock, and a mobile carriage (100) movable along the linear axis (x), the carriage carrying a light source (110) for directing a beam of collimated light across the x axis to be interrupted by the piece under measurement, the carriage further carrying an optical detector (120) aligned with the light source (110) and arranged to receive the residual light of the beam of collimated light that has not been interrupted by the piece under measurement. The measuring apparatus has an automatic measure mode or click mode (304) triggered by a button on the apparatus, that is arranged to automatically guess the features of a workpiece and/or recognize workpieces for which a measurement program is available.