Added the sample

SfChartMultipleTrackball/SfChartMultipleTrackball.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.11.35327.3
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "SfChartMultipleTrackball", "SfChartMultipleTrackball\SfChartMultipleTrackball.csproj", "{E5B30519-D065-42FC-B89A-B435C07011D9}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{E5B30519-D065-42FC-B89A-B435C07011D9}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E5B30519-D065-42FC-B89A-B435C07011D9}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E5B30519-D065-42FC-B89A-B435C07011D9}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E5B30519-D065-42FC-B89A-B435C07011D9}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {0CA07FB0-0F65-49F3-AFCC-11C28CE1D119}
+	EndGlobalSection
+EndGlobal

SfChartMultipleTrackball/SfChartMultipleTrackball/App.xaml

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+<Application x:Class="SfChartMultipleTrackball.App"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:local="clr-namespace:SfChartMultipleTrackball"
+             StartupUri="MainWindow.xaml">
+    <Application.Resources>
+
+    </Application.Resources>
+</Application>

SfChartMultipleTrackball/SfChartMultipleTrackball/App.xaml.cs

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+using System.Configuration;
+using System.Data;
+using System.Windows;
+
+namespace SfChartMultipleTrackball
+{
+    /// <summary>
+    /// Interaction logic for App.xaml
+    /// </summary>
+    public partial class App : Application
+    {
+    }
+
+}

SfChartMultipleTrackball/SfChartMultipleTrackball/AssemblyInfo.cs

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+using System.Windows;
+
+[assembly: ThemeInfo(
+    ResourceDictionaryLocation.None,            //where theme specific resource dictionaries are located
+                                                //(used if a resource is not found in the page,
+                                                // or application resource dictionaries)
+    ResourceDictionaryLocation.SourceAssembly   //where the generic resource dictionary is located
+                                                //(used if a resource is not found in the page,
+                                                // app, or any theme specific resource dictionaries)
+)]

SfChartMultipleTrackball/SfChartMultipleTrackball/MainWindow.xaml

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+<Window x:Class="SfChartMultipleTrackball.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:local="clr-namespace:SfChartMultipleTrackball"
+        mc:Ignorable="d"
+        Title="MainWindow" Height="450" Width="800"
+        xmlns:chart="clr-namespace:Syncfusion.UI.Xaml.Charts;assembly=Syncfusion.SfChart.WPF">
+
+    <Grid>
+
+        <chart:SfChart x:Name="chart" Header="Server CPU load by Day">
+
+            <chart:SfChart.PrimaryAxis>
+                <chart:CategoryAxis ShowTrackBallInfo="True"/>
+            </chart:SfChart.PrimaryAxis>
+
+            <chart:SfChart.SecondaryAxis>
+                <chart:NumericalAxis ShowTrackBallInfo="True" Minimum="0" Maximum="100"/>
+            </chart:SfChart.SecondaryAxis>
+
+            <chart:SfChart.Resources>
+                <Style TargetType="chart:ChartTrackBallControl" x:Key="trackballStyle1">
+                    <Setter Property="Background" Value="GreenYellow"/>
+                    <Setter Property="Height" Value="10"/>
+                    <Setter Property="Width" Value="10"/>
+                </Style>
+                <Style TargetType="Line" x:Key="lineStyle1">
+                    <Setter Property="Stroke" Value="Black"/>
+                    <Setter Property="StrokeThickness" Value="1.5"/>
+                </Style>
+
+                <Style TargetType="chart:ChartTrackBallControl" x:Key="trackballStyle2">
+                    <Setter Property="Background" Value="Orange"/>
+                    <Setter Property="Height" Value="10"/>
+                    <Setter Property="Width" Value="10"/>
+                </Style>
+                <Style TargetType="Line" x:Key="lineStyle2">
+                    <Setter Property="Stroke" Value="Black"/>
+                    <Setter Property="StrokeThickness" Value="1.5"/>
+                </Style>
+            </chart:SfChart.Resources>
+
+            <chart:SfChart.Behaviors>
+                <local:ChartTrackBallBehaviorExt x:Name="trackball1" ChartTrackBallStyle="{StaticResource trackballStyle1}" UseSeriesPalette="True" LineStyle="{StaticResource lineStyle1}"/>
+                <local:ChartTrackBallBehaviorExt x:Name="trackball2" ChartTrackBallStyle="{StaticResource trackballStyle2}" UseSeriesPalette="True" LineStyle="{StaticResource lineStyle2}"/>
+            </chart:SfChart.Behaviors>
+
+            <chart:LineSeries ItemsSource="{Binding Data}" XBindingPath="Day" YBindingPath="CPULoad" StrokeThickness="3" Interior="OrangeRed">
+                <chart:LineSeries.AdornmentsInfo>
+                    <chart:ChartAdornmentInfo Symbol="Ellipse" SymbolInterior="White" SymbolStroke="OrangeRed"/>
+                </chart:LineSeries.AdornmentsInfo>
+            </chart:LineSeries>
+
+        </chart:SfChart>
+
+    </Grid>
+
+    <Window.DataContext>
+        <local:ViewModel/>
+    </Window.DataContext>
+
+</Window>

SfChartMultipleTrackball/SfChartMultipleTrackball/MainWindow.xaml.cs

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+using Syncfusion.UI.Xaml.Charts;
+using System.Reflection;
+using System.Windows;
+using System.Windows.Input;
+
+namespace SfChartMultipleTrackball
+{
+    /// <summary>
+    /// Interaction logic for MainWindow.xaml
+    /// </summary>
+    public partial class MainWindow : Window
+    {
+        public MainWindow()
+        {
+            InitializeComponent();
+            trackball1.SfChart = this.chart;
+            trackball2.SfChart = this.chart;
+        }
+
+        protected override void OnContentRendered(EventArgs e)
+        {
+            base.OnContentRendered(e);
+
+            // Run the ShowTrackball method asynchronously
+            Task.Run(async () =>
+            {
+                await ShowTrackball();
+            });
+        }
+
+        async Task ShowTrackball()
+        {
+            // Wait for 1 second before executing the rest of the method
+            await Task.Delay(1000);
+            Application.Current.Dispatcher.Invoke(() =>
+            {
+                // Calculated positions for the first trackball
+                float xPosition = (float)chart.ValueToPoint(chart.PrimaryAxis, 1);
+                float yPosition = (float)chart.ValueToPoint(chart.SecondaryAxis, 169);
+
+                // Calculated positions for the second trackball
+                float xPosition1 = (float)chart.ValueToPoint(chart.PrimaryAxis, 6);
+                float yPosition1 = (float)chart.ValueToPoint(chart.SecondaryAxis, 170);
+
+                // Display the first trackball
+                trackball1.Display(xPosition, yPosition);
+
+                // Display the second trackball
+                trackball2.Display(xPosition1, yPosition1);
+            });
+        }
+    }
+
+    public class Model
+    {
+        public string Day { get; set; }
+        public double CPULoad { get; set; }
+    }
+
+    public class ViewModel
+    {
+        public List<Model> Data { get; set; }
+
+        public ViewModel()
+        {
+            Data = new List<Model>
+            {
+                new Model { Day = "Monday", CPULoad = 35 },
+                new Model { Day = "Tuesday", CPULoad = 42 },
+                new Model { Day = "Wednesday", CPULoad = 18 },
+                new Model { Day = "Thursday", CPULoad = 30 },
+                new Model { Day = "Friday", CPULoad = 64 },
+                new Model { Day = "Saturday", CPULoad = 22 },
+                new Model { Day = "Sunday", CPULoad = 10 }
+            };
+        }
+    }
+
+    public class ChartTrackBallBehaviorExt : ChartTrackBallBehavior
+    {
+        private bool isTrackballActive = false;
+
+        public SfChart SfChart { get; set; }
+
+        public double X { get; set; }
+        public double Y { get; set; }
+
+        protected override void OnMouseEnter(MouseEventArgs e)
+        {
+            // Get the position of the mouse pointer
+            var touchPoint = e.GetPosition(null);
+
+            // Find the nearest trackball to the mouse pointer
+            var trackball = FindNearestTrackball(touchPoint);
+
+            // Activate the trackball if it is the nearest one
+            if (trackball == this)
+            {
+                isTrackballActive = true;
+                base.OnMouseEnter(e);
+            }
+        }
+
+        protected override void OnMouseMove(MouseEventArgs e)
+        {
+            // Check if the trackball is activated
+            if (isTrackballActive)
+            {
+                // Get the position of the mouse pointer
+                var touchPoint = e.GetPosition(null);
+
+                // Display the trackball at the current mouse position
+                Display((float)touchPoint.X, (float)touchPoint.Y);
+                base.OnMouseMove(e);
+            }
+        }
+
+        protected override void OnMouseLeave(MouseEventArgs e)
+        {
+            // Deactivate the trackball
+            isTrackballActive = false;
+        }
+
+        private ChartTrackBallBehavior FindNearestTrackball(Point touchPoint)
+        {
+            ChartTrackBallBehavior nearestTrackball = null;
+            double minDistance = double.MaxValue;
+
+            // Iterate through all trackball behaviors to find the nearest one
+            foreach (var trackballBehaviour in SfChart.Behaviors)
+            {
+                if (trackballBehaviour is ChartTrackBallBehaviorExt trackball)
+                {
+                    // Calculate the distance between the trackball and the touch point 
+                    double distance = Math.Sqrt(Math.Pow(trackball.X - touchPoint.X, 2) + Math.Pow(trackball.Y - touchPoint.Y, 2));
+
+                    // Update the nearest trackball if the current one is closer
+                    if (distance < minDistance)
+                    {
+                        minDistance = distance;
+                        nearestTrackball = trackball;
+                    }
+                }
+            }
+
+            return nearestTrackball;
+        }
+
+        public void Display(float x, float y)
+        {
+            X = x; Y = y;
+            IsActivated = true;
+            var point = new Point(x, y);
+
+            // Set the internal property for the current point
+            SetInternalProperty(typeof(ChartTrackBallBehavior), this, point, "CurrentPoint");
+
+            // Trigger the pointer position changed event
+            base.OnPointerPositionChanged();
+
+            // Activate the trackball
+            InvokeInternalMethod(typeof(ChartTrackBallBehavior), this, "Activate", IsActivated);
+        }
+
+        // Sets an internal property of an object using reflection.
+        internal static void SetInternalProperty(Type type, object obj, object value, string propertyName)
+        {
+            var properties = type.GetRuntimeProperties();
+
+            foreach (var item in properties)
+            {
+                if (item.Name == propertyName)
+                {
+                    item.SetValue(obj, value);
+                    break;
+                }
+            }
+        }
+
+        // Invokes an internal method of an object using reflection.
+        internal static object? InvokeInternalMethod(Type type, object obj, string methodName, params object[] args)
+        {
+            var method = type.GetTypeInfo().GetDeclaredMethod(methodName);
+            return method?.Invoke(obj, args);
+        }
+    }
+}

SfChartMultipleTrackball/SfChartMultipleTrackball/Model/Model.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace SfChartMultipleTrackball
+{
+    public class Model
+    {
+        public string? Day { get; set; }
+        public double CPULoad { get; set; }
+    }
+}

SfChartMultipleTrackball/SfChartMultipleTrackball/SfChartMultipleTrackball.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0-windows</TargetFramework>
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <UseWPF>true</UseWPF>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Syncfusion.SfChart.WPF" Version="*" />
+  </ItemGroup>
+
+</Project>

SfChartMultipleTrackball/SfChartMultipleTrackball/SfChartMultipleTrackball.csproj.user

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+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="Current" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup />
+  <ItemGroup>
+    <ApplicationDefinition Update="App.xaml">
+      <SubType>Designer</SubType>
+    </ApplicationDefinition>
+  </ItemGroup>
+  <ItemGroup>
+    <Page Update="MainWindow.xaml">
+      <SubType>Designer</SubType>
+    </Page>
+  </ItemGroup>
+</Project>

SfChartMultipleTrackball/SfChartMultipleTrackball/ViewModel/ViewModel.cs

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+namespace SfChartMultipleTrackball
+{
+    public class ViewModel
+    {
+        public List<Model> Data { get; set; }
+
+        public ViewModel()
+        {
+            Data = new List<Model>
+            {
+                new Model { Day = "Monday", CPULoad = 35 },
+                new Model { Day = "Tuesday", CPULoad = 42 },
+                new Model { Day = "Wednesday", CPULoad = 18 },
+                new Model { Day = "Thursday", CPULoad = 30 },
+                new Model { Day = "Friday", CPULoad = 64 },
+                new Model { Day = "Saturday", CPULoad = 22 },
+                new Model { Day = "Sunday", CPULoad = 10 }
+            };
+        }
+    }
+}