The figure illustrates the application of the WG_M method to the LoS component of the 3D magnetic field skeleton of (a) AR 11166 (left) and (b) AR 12192 (right), respectively, to determine optimum forecasting height. The moments of starting and closest convergence (i.e., minimum) times are deduced by the maximum and minimum values, respectively, of the best nth degree polynomial fit to the D _pn data. The colour bar gives information about the actual value of D _pn . The grey zones are only indicative line formation heights.