Outlier statistics. The histograms show the distribution of the number of outliers, i.e., points with a quality flag < 0.9, per day for HARPS (green) and HARPS-N (red). The histograms are binned between one and 100 outliers per day in steps of one. The fraction of days is relative to the number of days observed with each instrument. For HARPS and HARPS-N, 47.3% and 76.1%, respectively, of all observed days have at least one outlier.