public partial class MainWindow : Window
    {
        private SignalPlot sp;
        private MarkerPlot HighlightedPoint = new();
        private int LastHighlightedIndex = -1;

        public MainWindow()
        {
            InitializeComponent();

            double[] yData = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
            WpfGraph.Plot.Clear();
            sp = WpfGraph.Plot.AddSignal(yData, 2);

            // Add a red circle we can move around later as a highlighted point indicator
            HighlightedPoint = WpfGraph.Plot.AddPoint(0, 0);
            HighlightedPoint.Color = System.Drawing.Color.Red;
            HighlightedPoint.MarkerSize = 8;
            HighlightedPoint.MarkerShape = MarkerShape.openCircle;
            HighlightedPoint.IsVisible = false;

            WpfGraph.Refresh();

            WpfGraph.MouseMove += WpfGraph_MouseMove;
        }

        private void WpfGraph_MouseMove(object sender, MouseEventArgs e)
        {
            (double mouseCoordX, double mouseCoordY) = WpfGraph.GetMouseCoordinates();
            (double pointX, double pointY, int pointIndex) = sp.GetPointNearestX(mouseCoordX);

//Incorrect pointIndex returned in v4.1.55 !
            //Debug.WriteLine("pointIndex = {0}", pointIndex);
            WpfGraph.Plot.Title("pointIndex = " + pointIndex);

            // place the highlight over the point of interest
            HighlightedPoint.X = pointX;
            HighlightedPoint.Y = pointY;
            HighlightedPoint.IsVisible = true;

            // render if the highlighted point chnaged
            if (LastHighlightedIndex != pointIndex) LastHighlightedIndex = pointIndex;

            WpfGraph.Refresh();
        }
    }