Vertical cuts along columns 230 (band 4A, top) and 760 (band 3A, bottom) of NGC 7027 images for the MIRIFULONG detector, subband A, before (blue) and after (orange) calibration by the flatfield and by the fringe flat derived from that source, as done in the JWST calibration pipeline. Each column is a spectrum in detector space, neglecting slice curvature and distortion (the spectrum of a fixed point in spatial coordinates would follow an iso-α line). The fringes are the strong periodic ripples in the spectral baseline. The peaks are emission lines from the source. Each fringe flat is normalised to have a maximum equal to unity, so the fluxes after fringe flat calibration follow roughly the fringe maxima (photometric calibration is performed in a later step in the JWST calibration pipeline).