Median (solid red line) and the variation as measured by the standard deviation (dashed red lines) of the cross-calibration bias parameter, J₂, of the sample obtained by the procedure laid out in Appendix B. The blue symbols indicate the corresponding values obtained from the cluster data (repeated from Fig. 5). The results for the MOS1/pn and MOS2/pn pairs are shown in the left and right panels, respectively. The horizontal dashed line indicates the expectation (unity) in the case of no cross-calibration bias.