As a function of apparent magnitude, we plot for each source the observed photometric scatter subtracted from the model and divided by the propagated uncertainty (ν in the vertical axis title is equal to ﹩\left(\nu ^{2}_{m,n}+\nu ^{2}_{m,\mathrm{model}\,}\right)^{1/2}﹩). Note that this is not equivalent to the subtraction in quadrature for the identification of source variability. Data are shown in black. The green vertical dashed lines correspond to the break point magnitudes. 5 σ horizontal lines are shown in red. Sources on this plot with y‐axis values of <−5 demonstrate that propagated uncertainties are underestimated by a factor of <2. Since we do not identify a source of additional uncertainty, we do not apply a correction factor. Instead, in § 3.5.2, we ensure that the identified variables are statistically robust. See § 3.2.4.