@Override
  protected void onStart() {
    super.onStart();
    connectionManager.connect();

    SharedPreferences preferences = getSharedPreferences(SettingsFragment.PREF_TUT_MEASURE, 0);
    boolean showTutorial = preferences.getBoolean(SettingsFragment.PREF_TUT_MEASURE, true);
    Log.d("iris", "boolean" + showTutorial);

    // if all devices are already connecting, start measuring
    if (connectionManager.getConnectedDevices().size() == devices.size() && !showTutorial) {
      startMeasurement();
    }
  }
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    //        setContentView(R.layout.activity_main);

    connectionManager = ConnectionManager.getInstance(this);
    connectionManager.setDevices(devices);
    connectionManager.setConnectionListener(this);

    evaluation = new HashMap<>();
    // create a new evaluation instance for each trackable device
    for (BluetoothDevice device : devices) {
      evaluation.put(device, new MovingAverageEvaluation());
    }
  }
 @Override
 protected void onStop() {
   super.onStop();
   stopMeasurement();
   connectionManager.disconnect();
 }