Uncertainty in parallax versus magnitude. Left: five-parameter solutions. Right: six-parameter solutions. The plots include all sources with G < 11.5 and a geometrically decreasing random fraction of the fainter sources, so as to give a roughly constant number of sources per magnitude interval. The colour scale from yellow to black indicates an increasing density of data points in the diagram. The curves show the 10th, 50th, and 90th percentiles of the distribution at a given magnitude.