Abstract: The orientation state of a film material is determined from the double refraction during the manufacturing process. A light source irradiates the film material to measure the path difference corresponding to the anisotropy of the film material. Interference patterns, created by one or more compensating wedges, are recorded by a photosensitive diode matrix. The individual electrical signals generated by the diode matrix are subjected to level discrimination by a discriminator and generated as binary images, each of which has a single interference stripe, which is evaluated. Interference patterns from different irradiation directions are simultaneously imaged next to each other and/or above one another. If an interference stripe cannot be found in a diode line, the system switches to the diode lines of the diode matrix which are above or below it. The thickness of the film material is measured and the double refraction calculated from it along with the path difference.