Throughput evolution of the astrometric fields of view (averaged over all AF CCDs) as a function of time as revealed by the G-band photometric time-link calibration derived in Riello et al. (2016). The curves are Chebyshev polynomials of the actual calibrations. Red lines refer to the preceding field of view; blue lines to the following field of view. The discontinuities and dotted vertical lines refer to the decontaminations (Sect. 6.4). OBMT stands for onboard mission timeline in units of six-hour revolutions since launch (Sect. 5.3.3). Gaia DR1 is based on data covering the interval OBMT = 1078.3795–2751.3518, delimited by the dashed black lines.