Evolution of the feature quantiles (q _i , where i is the feature index) and the feature coefficients (c _i , on the first principal component) of the target (KN of GW170817; matched by coordinate within 1″). The X-axis corresponds to individual exposures in chronological order (four exposures here), and we omit the exact exposure number (or observation time) for clarity. The circular marker color shows the PSF flux S/N (a redder color corresponds to a higher S/N) on the difference image. The gray squares give the coefficients of a feature on the first principal component for different exposures; the hollow squares give the (sign flipped) negative values; the horizontal dotted line shows one divided by the square root of the number of features. We also present the time evolution of the first component EVR, the quantile of the first component value of the target compared to other sources (q _P), and the teff (τ). Additionally, we give the mean coefficient value 〈c _i 〉, with the fraction of positive values (f ₊), and the mean quantile value 〈q _i 〉 among exposures. The gray curve in the q _P diagram gives the mean of all feature quantiles of the target, in order to test the effectiveness of PCA candidate selection.