chart_item_init (&npp->chart_item, &np_plot_chart_class, label);
npp->data = casereader_clone (reader);
npp->y_min = np->y_min;
chart_item_init (&npp->chart_item, &np_plot_chart_class, label);
npp->data = casereader_clone (reader);
npp->y_min = np->y_min;