\section{Scanning law}

The Gaia satellite consist of two telescopes, which are projected onto one focal plane. The time between the two fields of view being observed is 106.5 mins and then the time between subsequent scans is 6 hours. After these initial observations the field will be revisited every $\sim$10-30 days. Over the full mission each patch of sky will be measured, on average, approximately 70 times. The densest coverage is at 45 degrees to the ecliptic plane and this region is covered with approximately 200 epochs.