def on_clear(self, event):
        """
        initialize window to allow user to empty the working directory
        """
        dia = pmag_menu_dialogs.ClearWD(self.parent, self.parent.WD)
        clear = dia.do_clear()
        if clear:
            # clear directory, but use previously acquired data_model
            if self.data_model_num == 2.5:
                self.parent.er_magic = builder.ErMagicBuilder(self.parent.WD, self.parent.er_magic.data_model)
            elif self.data_model_num == 3:
                self.parent.contribution = cb.Contribution(self.parent.WD,
                                                           dmodel=self.parent.contribution.data_model)