Top: example of a good track fitting the differential lightcurve Δm_AD observed for the C iv broad line and for the continuum. Centre: corresponding tracks (solid line) in the microlensing pattern of image A (left) and D (right). The large circle represents the C iv source size and the small one the continuum. Bottom: track corresponding to the continuum emission (red solid line) and to the C iv emitting region (dashed grey line) for image A (left) and D (right).