Evolution in time of the geometric calibration, relative to the nominal geometry, evaluated at the centre of the CCD in the across-scan direction and for different CCDs (BP in the top panel, RP in the bottom panel; rows from 1 to 7 are shown in red, orange, yellow, green, blue, purple, and pink). The preceding FoV is shown with brighter colours and solid lines, while darker shades and dashed lines are used for the following FoV, as indicated by the labels P and F in the plot area.