Standard deviation versus G magnitude for light curves in the GAPS (top) and YSO (bottom) samples. The colour bar indicates source counts. The solid blue line marks the 97th percentile for the GAPS sample, and the hatched region identifies YSO sources lying below this percentile (secondary sample), while primary-sample sources lie above it. In both panels, the black dashed line shows the lower envelope (1st rolling percentile) of the YSO distribution to aid visual comparison.