def ms_cutlo(self, viewer, event, data_x, data_y):
        """An interactive way to set the low cut level.
        """
        if not self.cancut:
            return True

        x, y = self.get_win_xy(viewer)

        if event.state == 'move':
            self._cutlow_xy(viewer, x, y)

        elif event.state == 'down':
            self._start_x, self._start_y = x, y
            self._loval, self._hival = viewer.get_cut_levels()

        else:
            viewer.onscreen_message(None)
        return True
An interactive way to set the low cut level.