private void _chartControl_MouseDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
      System.Windows.Point point = e.GetPosition(_chartControl);
      NCartesianChart chart = (NCartesianChart)(_chartControl.Charts[0]);
      NViewToScale2DTransformation transf = new NViewToScale2DTransformation(_chartControl.View.Context, chart, (int)StandardAxis.PrimaryX, (int)StandardAxis.PrimaryY);
      NVector2DD pointScale = default(NVector2DD);
      transf.Transform(new NPointF((float)point.X, (float)point.Y), ref pointScale);
 }