The interferometric length measurement value in multi-axis positioning and measuring systems is directly influenced
by the topography of reference mirrors. Form deviations of the mirror plane can cause systematic
measurement errors because the specimen geometry is superimposed upon the topography of reference mirrors.
This article discusses the complete acquisition of the topography of a special mirror arrangement with the help
of a Fizeau interferometer to correct systematic measurement errors after the raw measurement using the expanded
three-flat test. Furthermore, other influencing factors are presented in the article, e.g., measurement
errors caused by the Fizeau interferometer. Additionally, temporal changes of the reference mirror topography
are detected by regularly occurring measurements, and the topography data used as the correction reference are