Histograms of sky flux measurements in empty apertures of 0.″4 diameter in the GOODS-S field. The top panel shows the measurement for the F275W filter, while the bottom shows F336W fluxes. They have been normalized to a common zero-point of 25 mag to facilitate the comparison. The different curves represent different surveys. Despite longer exposure times, the UVUDF is slightly shallower than the HDUV data due to problems with uneven background (see the text for details). The gains relative to the short ERS exposures of both the HDUV and the UVUDF in the F275W filter are reduced due to the need for post-flash observations.