Synthetic circular polarization for selected objects from the CFHT archive. As in Fig. 12, the highest levels are shown. The gray zone indicates a one-sigma dispersion around the mean value: − 0.01 ± 0.21%, for objects with IT ≥ 20 s. This limit is indicated by a vertical dashed line. The objects measured using the old ADC (in 2006−2008 interval) are shown with magenta dots. The more recent measurements are shown with black dots.