Increases the zoom of the graph one step (0.1 units).

def ScaleLarger(self):
    """Increases the zoom of the graph one step (0.1 units)."""
    newfactor = self._zoomfactor + 0.1
    if float(newfactor) > 0 and float(newfactor) < self._MAX_ZOOM:
      self._zoomfactor = newfactor