Three examples of confidence contours (Δχ² = + 0.5,−2.3,−4.61, and −9.21 for the black, red, green, and blue contours, respectively) of energy vs. intensity of a narrow emission/absorption line between 3−10 keV during observations M2 (top panel), M10 (middle panel), and M3 (bottom panel). These illustrate the typical intensity of residuals left in the observation-by-observation best-fit spectra around 6−8 keV with (top and middle panels) and without residuals left (bottom panel).