(a) SOHO/MDI magnetograms of AR 10268. The magnetograms have the same contours and colour convention as described in Fig. 7a. (b) Evolution of the AR magnetic flux computed from the magnetograms (black-solid line). The vertical-dashed line marks the time at which the AR 10268 reaches its maximum flux. (c) Evolution of ϕ_a derived from the magnetic barycentres and ϕ_c obtained with CoFFE (see inset). The drawing conventions are the same as in Fig. 7. The associated movie is available online (fig8_a.avi).