private double getAngle(double xTouch, double yTouch) {
  double x = xTouch - (dialerWidth / 2d);
  double y = dialerHeight - yTouch - (dialerHeight / 2d);
  double angle = Math.atan2(y,x) * 180 / Math.PI;
  if( angle<0 ) angle += 2 * Math.PI;
  return angle;
}

    private final static float FLING_SPEED = 0.4;

    private class MyGestureDetector extends SimpleOnGestureListener {
        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    
            double x1 = e1.getX() - (dialerWidth / 2);
            double y1 = dialerHeight - e1.getY() - (dialerHeight / 2);
            
            double x2 = e2.getX() - (dialerWidth / 2);
            double y2 = dialerHeight - e2.getY() - (dialerHeight / 2);
            
            float speed = (float)(Math.sqrt( velocityX * velocityX + velocityY * velocityY ) * FLING_SPEED);

            float dir = (float)Math.signum( y1 * x2 - x1 * y2 );
            // Berechnung der Orientierung der Drehung anhand der Determinate von
            // Anfang und Ende des Flings.
            
            dialer.post( new FlingRunnable( dir * speed ));
            
            return true;
        }
    }