Illustration of the effects of calibration and sky emission subtraction. The top panel shows raw data from the MASCARA-1 b data set of a section of one order. Bad pixels are marked in white. Sky emission lines appear as tilted lines with excess flux. The vertical bands are detector readout artifacts, some of which remain after dark subtraction. The middle panel shows the same data that have been calibrated and where the vertical bands have been estimated and removed by subtraction (before dividing by the flat field). The bottom panel shows the result of sky emission subtraction using the ExoRES pipeline. The units are ADUs.