(a) Evolution of the magnetic flux computed from the synthetic magnetograms for the FR model with uniform twist (N_t, 0 = 0.5, h = g = 0) during its emergence. We plot the magnetic flux [F_z] (black line), the axial flux [] (green line), and the azimuthal flux [] (blue line). All fluxes are computed for the z component of the fields. All fluxes are normalised to the maximum axial FR flux. (b) Evolution of the apparent tilt ϕ_a computed from the magnetic barycentres (on the full magnetogram, black line) and ϕ_c using CoFFE with p = 0 for two n_it values (see the inset). The coloured-shaded area surrounding the red line represents the ϕ_c range obtained for different values of p within the interval [−1, 1] after the convergence criterion of the tilt angle is achieved.