public partial class MainWindow : Window
{
	private readonly IHasPoints plottable;
	private readonly ScatterPlot HighlightedPoint;
	private int LastHighlightedIndex = -1;

	public MainWindow()
	{
		InitializeComponent();

		int sampleCount = 50;
		double[] xs = new double[sampleCount];
		double[] ys = new double[sampleCount];

		Random rand = new Random(0);
		for (int i = 0; i < 50; i++)
		{
			xs[i] = DateTime.Now.ToOADate() + i*10;
			ys[i] = i > 0 ? ys[i - 1] + rand.NextDouble() - .5 : 0;
		}

		//plottable = plot.Plot.AddScatterPoints(xs, ys);    // <-- this works as expected
		plottable = plot.Plot.AddSignalXY(xs, ys);
			
		HighlightedPoint = plot.Plot.AddPoint(0, 0);
		HighlightedPoint.Color = System.Drawing.Color.Red;
		HighlightedPoint.MarkerSize = 10;
		HighlightedPoint.MarkerShape = MarkerShape.openCircle;
		HighlightedPoint.IsVisible = false;

		plot.Plot.XAxis.DateTimeFormat(true);
	}

	private void plot_MouseMove(object sender, MouseEventArgs e)
	{
		(double mouseCoordX, double mouseCoordY) = plot.GetMouseCoordinates();

		// these results are incorrect when plottable is SignalPlotXY:
		(double pointCoordX, double pointCoordY, int pointIndex) = plottable.GetPointNearestX(mouseCoordX);

		// highlight the point of interest
		HighlightedPoint.Xs[0] = pointCoordX;
		HighlightedPoint.Ys[0] = pointCoordY;
		HighlightedPoint.IsVisible = true;

		tbPointCoord.Text = $"{pointCoordX:N1}, {pointCoordY:N1}";
		tbIndex.Text = pointIndex.ToString();

		if (LastHighlightedIndex != pointIndex)
		{
			LastHighlightedIndex = pointIndex;
			plot.Render();
		}
	}
}