How to apply label formatting to trackball labels in WPF Chart (SfChart)?

<chart:SfChart>
      <chart:SfChart.Resources>
            <local:LabelConverter x:Key="labelConverter"/>
            <DataTemplate x:Key="trackBallTemplate">
                   <Border BorderBrushn="Black” BorderThickness="1”>
                          <Grid Height="30”>
                                <Grid.ColumnDefinitions>
                                      <ColumnDefinition>
                                      <ColumnDefinition>
                                 <Grid.ColumnDefinitions/>
                                 <Rectangle Fill="White” Grid.ColumnSpan="2”/>
                       <Ellipse Fill="Green” Margin="3” Height="20” Width="20”/>
                                 <TextBlock Margin="3”  Grid.Column="1”>
                                         Text="{Binding 
                                         Converter="{StaticResource labelConverter }"}"/>
                          <Grid/>
                   <Border/>
            <DataTemplate/>
      <chart:SfChart.Resources/>
      <chart:SfChart.Behaviors>
              <chart:ChartTrackBallBehavior/>
      <chart:SfChart.Behaviors/>
      <chart:LineSeries TrackBallLabelTemplate="{Binding trackBallTemplate}"
                                   XBindingPath="Year" YBindingPath="Count"
                                   ItemsSource="{Binding}"/>  
<chart:SfChart/>

public class LabelConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var pointValue = value as ChartPointInfo;
        double d = double.Parse(pointValue.ValueY.ToString());
        return d.ToString("0.000000");
    }
}