log L_X residuals of the 313 clusters as a function of their RASS exposure time (upper left), total hydrogen column density (upper center), flux (upper right), redshift (bottom left), statistical uncertainty (bottom center) and outer metallicity (bottom right). The best-fit relation between the residuals and these quantities is also plotted with its 1σ uncertainty (green area). The black line represents the best-fit model for the full sample against which the residuals are calculated.