Centroid determination of O VII (top) and O VIII (bottom) lines. In both panels, we display the probability distribution functions for the centroid energy of all regions where both lines were detected with at least 10σ significance. The vertical black lines mark the mean line centroid energies, constructed via a weighted average over all regions, and the shaded areas indicate the corresponding 3σ uncertainties. The color scale reflects the mean centroid energies, purely for the purpose of visual differentiation.