Electronic offset level in AF2 on row 4 of the Gaia focal plane. Mean values of the approximately hourly bursts of prescan data are plotted in red. The upper locus is for hardware-binned CCD samples containing 12 pixels AC, while the lower locus is for unbinned data. The dip in offset level near 1320 revolutions resulted from an onboard electronic disturbance caused by activation of payload module heaters during a decontamination period. One revolution of Gaia takes 6 h and so the x-axis covers roughly 118 days from 19th August 2014 to 15th December 2014. One ADU corresponds to 3.9 e⁻.