The Line Spread Function (LSF) is a convolution of the response functions of the mirror and the grating, followed by convolution with the detector response. The mirror response is approximated by a Lorentzian profile, which has been calibrated against observations of PKS 0312-770. The grating response depends on the accuracy of the variable line density of the gratings, the figure errors of the gratings, their alignment, and the scattering of X-rays due to surface roughness, this latter seen as the horizontal distribution of events in the bottom panel of Fig. 77. Two scattering components have been identified: a small angle scale Gaussian component, and a large scale Lorentzian component. The wings in the LSF are reduced by applying an energy selection in the CCD response. The effect of this selection is asymmetric, as shown