Example of adjusting Swift-UVOT fluxes, for the U-band. The magnitudes of two standard stars are shown in the top two panels (the magnitude of the first standard star could not be extracted for the fourth epoch). We assume the flux of these objects to be constant over the time covered by the Swift observations. We calculate the difference with the mean flux (indicated by the dashed line) for the observed flux in each epoch and adjust the magnitudes for J234402 accordingly. The bottom panel shows the uncorrected (grey) and corrected (open) magnitudes for the U-band observations of J234402.