code: def _onLeftButtonUp(self, evt):
          
          x = evt.GetX()
          y = self.figure.bbox.height - evt.GetY()
          #print 'release button', 1
          evt.Skip()
          if self.HasCapture(): self.ReleaseMouse()
          FigureCanvasBase.button_release_event(self, x, y, 1, guiEvent=evt)
docs: End measuring on an axis.