Bottom panel: Evolution of the equivalent width (in Å) of representative emission lines as a function of time, calculated from the spectra of MAXI J1820+070 in Fig. 11. Top panel: Ratio between the equivalent widths of two of these lines, HeII 4686 Å and Hβ. The colour bar on the top indicates the value of the B band magnitude of the source at the time of the observations. We show for comparison also the periods where the optical (grey shaded area) and the X-ray (orange shaded area) modulation are seen in the light curves, together with the epochs of the different accretion states that the source entered (Shidatsu et al. 2019).