In a process or device for very accurate determination of the plane of polarization of polarized light, the light from a light source is polarized by means of a polarizing filter which has a certain setting angle 0 with respect to the first reference plane, the plane of incidence on the reflecting surface. At least one surface of the panel member has a pattern of light extracting deformities formed by applying the deformities to the panel member and afterward permanently attaching the deformities to the panel member to become part of the assembly. The rate of retraction and extension of all cylinders is controlled by felt strips restricting the flow of air between the cylinders. Such calculation operations include determining a corresponding normal vector for each component primitive vertex.