Distribution of residuals for the satellite between the observed (index o) and predicted(index c) positions, normalized by the uncertainty on the measured positions (σ), and color-coded by observing epoch. X stands for right ascension and Y for declination. The three large gray circles represent the 1, 2, and 3 σ limits (typically 10 mas at 1 σ). Top panel: histogram of residuals along X. Right panel: residuals along Y. The light gray Gaussian in the background has a standard deviation of one.