Difference between the reference Gaia DR2 catalogue and the measured RA (top panel) and Dec (bottom panel) of sources in the EDF-N channel 1 mosaic with 16 < [3.6] < 19 total magnitudes as a function of the coordinate. The solid red line shows a running median computed in bins of 20 points, and the shaded areas indicate the regions containing 68% and 99% of all sources, respectively.