Covariance between formation redshift and X-ray luminosity residuals, with and without gas fraction corrections. Left panel: formation redshift (16,50,86 percentile) at fixed mass for clusters with L_X, ce that is not corrected for gas, split into three tertiles. Middle panel: formation redshift (16,50,86 percentile) at fixed mass for a cluster with gas-corrected L_X, ce split into three tertiles. Right panel: concentration (16,50,86 percentile) at fixed mass for a cluster with gas-corrected L_X, ce split into three tertiles.