code: def ms_cutlo(self, viewer, event, data_x, data_y):
          
          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
docs: An interactive way to set the low cut level.