Left panel: logarithmic luminosity uncertainty as a functionof the X-ray bolometric luminosity L_X, together with the correction limit (green line). Right panel: the best-fit normalization value for the entire sample (with the slope fixed to its best-fit value) as a function of the sample percentage in which an extra L_X uncertainty is added. The blue point and the green line represent the sample percentage that we use and the best-fit value we derive.