Cross correlation function (normalized to peak intensity) of F₂/F₁ with F₁ in the case of a time-lagged BLR (thin blue line) and of a non-variable BLR (dashed black). The third curve (thick solid black line) shows the CCF between the fraction of the quasar flux affected by (free of) microlensing F_Mμ (F_M), as obtained by linearly combining F₁ and F₂ (Sect. 2.4, Eq. (5)). The dotted-dashed vertical line shows the fiducial time lag τ = 100 days between the variation of the continuum and of the BLR in the simulation.