Histogram of differences between photometric and spectroscopic X-ray fluxes at 2 keV, shown in units of standard deviations. The red line shows the results of a Gaussian fit, which shows that the distribution is centred around zero. There is no significant skewness, as the skewness parameter turns out to be k = 0.27 ± 0.30. This shows that there is no systematic shift between the two quantities.