Comparison of Suzaku and XMM-Newton data residuals. Up: data residuals from the identical underlying model consisting of an absorbed power law and a Gaussian line. Bottom: data residuals from the final model containing an additional absorber with different covering fraction and slightly different slope of the power law for the XMM-Newton and the Suzaku observation. The front-illuminated spectra of XIS 0 and XIS 3 are jointly shown by black data points, the back-illuminated XIS 1 are red, and the EPIC-pn data are blue and emphasised by small circles. The data are binned for plotting purposes only.