The invention relates to a medical registration apparatus (1), comprising •two flanks (2a, 2b)； •a pivot portion (3) around which at least one of the flanks (2a, 2b) is rotatable with respect to a rotation centre (3c, 3d) (FIG. 1, FIG. 3)； •a contacting portion (4a, 4b) on each of the flanks (2a, 2b), each contacting portion (4a, 4b) being spaced apart from the rotation centre (3c, 3d)； and •a sensor (5, 6) being arranged with an offset (r, FIG. 4 A) to a line (a) connecting the contacting portions (4a, 4b). The invention also relates to a data processing method for use with the medical registration apparatus.
