Normalized ΔBIC vs. aperture size for candidate sets of covariates. For each aperture size, the ΔBIC values are computed relative to the BIC of the best-fit model without any covariates other than a linear trend with time. The most negative values of ΔBIC for each aperture size indicate the most preferred set of detrending covariates by that model selection criterion, but can only be compared to the other ΔBIC values at the same aperture size. Vertical shading highlights the aperture size that minimized the rms scatter, as described in Section 3.1.