/** @return spinner_rotation */
 private JSpinner getSpinner_rotation() {
   if (spinner_rotation == null) {
     spinner_rotation = new JSpinner();
     spinner_rotation.setMaximumSize(new Dimension(80, 27));
     spinner_rotation.setMinimumSize(new Dimension(80, 27));
     spinner_rotation.setPreferredSize(new Dimension(80, 27));
     spinner_rotation.setModel(
         new SpinnerNumberModel(0.0, -Double.MAX_VALUE, Double.MAX_VALUE, 1));
     spinner_rotation.setValue(TwoAxes3D.getRotation());
     spinner_rotation.addChangeListener(
         new ChangeListener() {
           @Override
           public void stateChanged(ChangeEvent e) {
             TwoAxes3D.setRotation((Double) spinner_rotation.getValue());
             fireActionEvent(
                 new ActionEvent(
                     TwoAxes3DSettingsPanel.this,
                     0,
                     SycamoreFiredActionEvents.UPDATE_AGREEMENTS_GRAPHICS.name()));
           }
         });
   }
   return spinner_rotation;
 }