Density map of the variability amplitude proxy (ordinate) versus G magnitude (abscissa) for a random sample of 100 million Gaia DR2 sources that have at least five measurements in G_BP and G_RP. A dotted, dashed and solid horizontal red line is plotted as eye-guides at A_proxy, G = 0.30, 0.15, and 0.06, respectively. They correspond approximately to peak-to-peak amplitudes in G of 1 mag, 0.5 mag, and 0.02 mag, respectively. Vertical continuous blue lines are plotted at G = 5.5 mag and 19 mag, which define the magnitude limits of the sample studied in this paper. Additionally, a vertical dashed blue line is plotted at 18.5 mag.