Plotting may be done on multiple levels. Individual dataset may be plotted through dataset_plot...() methods. The datasets joined in the series may be plotted individually by using plot_series_datasets(). All datasets on a single graph for a series are obtained through plot_1D_series(). You may also explore influence of a specific parameter using grid_plot_series() with accept_better_parameter='discard' (so not to change your parameter set. With value 'accept' this method works as a manual fitting device - it will change current value of this parameter to the grid value giving sum of squares of residuals better than current one (if there is one, of course). If you want to explore dependence of the model on particular parameter values you better see the model curves without data (to have less clutter on the graph): use which_plots='model-only' (instead of 'all').
Plotting ranges for the datasets may be set by calling datasets' method set_XY_ranges(). Plotting ranges for the entire series may be set using set_XY_ranges_series()
For a specific usage see TotalFit.m