Study of the stability of the compass detector during data-taking In several physics topics the data analysis in COMPASS relies strongly on the stability of the detector performance during data taking. The analyses of different indicators for the spectrometer performance allow us to find time periods with very little changes in the detector. In addition single spills with low performance due to read out problems in data taking can be found and excluded from physics analysis. The goal of the project is to develop and study such indicators. It involves a study of the interplay of the different detectors of the SPECTROMETER and their effect on the data reconstruction. In addition it gives insights into the different physics subjects for COMPASS.