  Gaia will perform astrometric measurements with an unprecedented resolution.
Consequently, the electronics of the Astro instrument must time tag every
measurement with a precision of a few nanoseconds. Hence, it requires a high
stability clock signal, for which a Rb-type spacecraft master clock has been
baselined. The distribution of its signal and the generation of clock
subproducts must maintain these high accuracy requirements. We have developed a
software application to simulate generic clock frameworks. The most critical
clock structures for Gaia have also been identified, and its master clock has
been parameterised.
