Formal uncertainties versus the G magnitude for sources with a five-parameter astrometric solution. Left: semi-major axis of the error ellipse in position at epoch J2015.5. Middle: standard deviation in parallax. Right: semi-major axis of the error ellipse in proper motion. The yellow dots show individual values for a representative selection of the sources; the cyan curve is the median uncertainty and the blue curves are the 10th and 90th percentiles. The plotted sample contains all sources for G < 11, and a geometrically decreasing random fraction of the fainter sources with roughly uniform distribution in G.