Results of the fitting of the variations affecting a given pixel for a region encompassing the lines shown in Fig. 12. The zero point and the amplitude of the fitting function are shown in each panel. The amplitude is arbitrarily shifted along the ordinate axis and multiplied by 30 for visibility purposes. To allow for a more robust normalisation of Hg iiλ3984, the red wing of Hϵ was used to define pseudo-continuum regions.