Distribution of the uncertainty on the weighted mean G (top panel), G_BP (central panel), and G_RP (bottom panel) as a function of the G, G_BP, and G_RP magnitude, respectively. Only sources with ≈20 transits (corresponding to ≈200 CCD observations in G) have been included in this analysis. The black dotted line shows the expected uncertainties for sources with 200 G-band (20 G_BP, G_RP) contributions for a nominal mission with no calibration error. The dashed dark line shows the same expected uncertainties with an additional calibration error on the single measurement of 2.0 mmag for G-band, 3.1 mmag for G_BP and 1.8 mmag for G_RP added in quadrature. The Gaia DR1 and DR2 uncertainties are shown for comparison.