Residuals of a small wavelength interval after subtracting the average spectrum. The top panel shows the residuals obtained from the ExoRES pipeline. The middle panel shows the residuals obtained from the CR2RES pipeline using an 800-pixel swath width and with subtract_nolight_rows turned off. The bottom row shows the same as the middle row but with subtract_nolight_rows turned on. The data are from the MASCARA-1 b observation. The units are normalized flux, where the continuum level is set to match the telluric transmission before the average spectrum subtracting.