Temporal evolution of the absorption minima of the Hα, Hβ, and Fe II lines for non-microlensed and microlensed spectra using the two different magnification maps of Fig. 4 (left: Fig. 4a; right: Fig. 4b). For the microlensed spectra without noise (labeled S/N = ∞), the median of the 10 000 positions and the 1σ and 2σ ranges are shown in black and gray, respectively. The temporal evolution of the absorption lines with added noise of S/N = 10 is shown in orange and red.