The invention relates to a method for determining at least one influencing variable acting on the eccentricity in a goniometer, using a detector arrangement consisting of four optical detector elements, and a rotational body comprising a plurality of pattern elements arranged around a pattern center, the rotational body being rotatably arranged about an axis. According to said method, at least some of the pattern elements are reproduced on the detector arrangement, the positions of the pattern elements reproduced on the detector arrangement are resolved, and the eccentricity of the pattern center in relation to a detector center of the detector arrangement is determined. A plurality of such eccentricity measurements for different rotational positions enables different influencing variables acting on the current eccentricity to be separated, especially by forming units.