The following list of concepts might be useful for a good understanding of the
content of this chapter:
CCD transit, the transit of a source across one single CCD.
FoV transit, the complete transit of a source across the focal plane, this may include one SM transit, 9 (or 8) AF CCD transits, one BP transit and one RP transit. The RVS CCD transit is irrelevant for this chapter.
Source catalogue, the catalogue formed by all sources observed by Gaia. This is updated at each cycle. The catalogue used in cycle N is the one generated by the MDB Integrator at the end of cycle N-1.