Distribution of MAD as a function of median synthetic magnitude (i_η) for stars in the training sample. The dashed red curve shows the median MAD at varying median magnitudes, while the black curve shows the threshold for selecting optically variable sources (i.e., $\overline{\mathrm{MAD}}+3{\sigma }_G$). This threshold was estimated from the median MAD per magnitude bin plus three times the robust standard deviation (σ_G = 1.4826 × MAD) within each bin, interpolated using a fourth-order polynomial law. The vertical dashed black line marks the brightness limit at magnitude 20.5, beyond which noise increases significantly. The vertical dashed light lines indicate the binning used in the analysis.