SB limits obtained with the various methodologies plotted against sky brightness for the four Euclid bands. For the method that does not directly give sky brightness [Approach (1)], we used the mean of the sky values from Approaches (2) and (3). There is a correlation of the SB limits with sky brightness, with brighter sky having brighter limits, and a variation with methodology, up to 0.3-0.4mag arcsec^-2.