Saturation levels (measured in LSB, Least Significant Bit) for the AF CCD of strip 3 and row 3. The dashed vertical lines show the borders of the 16 stitch blocks for which magnitude intervals for the activation of the gates are determined. Most of the CCDs show saturation level variations of less than 10 000 LSB. Large areas of the CCD are dominated by analogue-to-digital conversion saturation and only at both edges image area saturation is dominating.