Abstract: Disclosed is a measuring instrument for determining geometric properties of a profiled element. Said measuring instrument comprises:—a device that generates at least one first light beam (7) and a second light beam (8), the direction of radiation of the first light beam being different from the direction of radiation of the second light beam;—a retro-reflecting surface (3) which is arranged in such a way relative to the light source that at least some of both light beams is incident on the retro-reflecting surface; and—a recording device (14) which can determine, across the transversal extension thereof, the light intensity distribution of at least some of the reflected light beam of the first light beam and at least some of the reflected light beam of the second light beam, the first light beam being reflected by the retro-reflecting surface and the second light beam being reflected by the/a retro-reflecting surface.