Effective area verified preflight by end-to-end measurements at the Panter facility (den Herder et al. 2001). This can be compared with the measured in flight effective area as verified on celestial sources (Fig. 34). The model is indicated by the solid line. Sharp features are caused by either atomic absorption edges or differences between different CCD Al layers. The broken lines indicate the relevant atomic edges. The asterisk symbols show the measured data points.