Median values following outlier removal as a function of stellar effective temperature. Black dots are for F-, G-, and K-type stars, and open blue squares are for M-type stars. The red error bars indicate the standard deviation of the measurements, while the grey error bars indicate the minimum and maximum values collected from the literature and following outlier removal. For stars with a single measurement, the standard deviation is the median value of the standard deviation obtained for all stars in the sample and shown by the dashed red line in Fig. 2.