MS Chart tooltip on mouse hover a point

// This code sample describes how to show a tooltip owhen the mouse cursor hovers a data.point.
// How To Run:
// 1 - Create a WinForms project called WinFormTests
// 2 - Double-click on Form1, add a MS chart (Dock = Fill)
// 3 - Open Form1.cs and copy and paste the following code
// 4 - Build and run

using System;
using System.Collections.Generic;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Windows.Forms;
using System.Windows.Forms.DataVisualization.Charting;

namespace WinFormTests
{
    public partial class Form1 : Form
    {
        internal class Item
        {
            public double X { get; private set; }
            public double Y { get; private set; }
            public Item(double x, double y)
            {
                this.X = x;
                this.Y = y;
            }
        }

        public Form1()
        {
            InitializeComponent();
            this.chart1.MouseMove += new MouseEventHandler(chart1_MouseMove);
            this.tooltip.AutomaticDelay = 10;
            FillChart();
        }

        private void FillChart()
        {
            var rand = new Random(123);
            var items = Enumerable.Range(0, 20).Select(x => new Item(x, rand.Next(1, 100) / 2.0)).ToList();

            this.chart1.Series.Clear();

            var seriesLines = this.chart1.Series.Add("Line");
            seriesLines.ChartType = SeriesChartType.Line; //System.Windows.Forms.DataVisualization.Charting.SeriesChartType.Line;
            seriesLines.XValueMember = "X";
            seriesLines.YValueMembers = "Y";
            seriesLines.Color = Color.Red;

            var seriesPoints = this.chart1.Series.Add("Points");
            seriesPoints.ChartType = SeriesChartType.Point; //System.Windows.Forms.DataVisualization.Charting.SeriesChartType.Line;
            seriesPoints.XValueMember = "X";
            seriesPoints.YValueMembers = "Y";

            this.chart1.DataSource = items;
        }


        Point? prevPosition = null;
        ToolTip tooltip = new ToolTip();

        void chart1_MouseMove(object sender, MouseEventArgs e)
        {
            var pos = e.Location;
            if (prevPosition.HasValue && pos == prevPosition.Value)
                return;
            tooltip.RemoveAll();
            prevPosition = pos;
            var results = chart1.HitTest(pos.X, pos.Y, false,
                                            ChartElementType.DataPoint);
            foreach (var result in results)
            {
                if (result.ChartElementType == ChartElementType.DataPoint)
                {
                    var prop = result.Object as DataPoint;
                    if (prop != null)
                    {
                        var pointXPixel = result.ChartArea.AxisX.ValueToPixelPosition(prop.XValue);
                        var pointYPixel = result.ChartArea.AxisY.ValueToPixelPosition(prop.YValues[0]);

                        // check if the cursor is really close to the point (2 pixels around)
                        if (Math.Abs(pos.X - pointXPixel) < 2 &&
                            Math.Abs(pos.Y - pointYPixel) < 2)
                        {
                            tooltip.Show("X=" + prop.XValue + ", Y=" + prop.YValues[0], this.chart1,
                                            pos.X, pos.Y - 15);
                        }
                    }
                }
            }
        }
    }
}