How Do I Consume Wcf Through Teleik Radcartesianchart On Windows Phone

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XAML

i have written a wcf service:

    public List<string> GetECGValue()
    {
        var query2 = (from r in obj.ECGs where (r.Reading_ID >= 1 && r.Reading_ID <= 10) select r.Value).ToList();
        return query2;
    }

    DataClasses1DataContext obj = new DataClasses1DataContext();
}

and this is the chart where i need to bind this service:

<chart:LineSeries x:Name="C" Stroke="Orange" StrokeThickness="2" ItemsSource="{Binding}">

                        <!--<chart:LineSeries.DataPoints>
                            <chartEngine:CategoricalDataPoint Value="20"/>
                            <chartEngine:CategoricalDataPoint Value="40"/>
                            <chartEngine:CategoricalDataPoint Value="35"/>
                            <chartEngine:CategoricalDataPoint Value="40"/>
                            <chartEngine:CategoricalDataPoint Value="30"/>
                            <chartEngine:CategoricalDataPoint Value="50"/>
                        </chart:LineSeries.DataPoints>-->
                    </chart:LineSeries> 

ServiceReference1.Service1Client ser = new ServiceReference1.Service1Client();
        public GraphECG()
        {
            InitializeComponent();
            ser.GetECGValueCompleted += new EventHandler<GetECGValueCompletedEventArgs>(ser_GetECGValueCompleted);
            ser.GetECGValueAsync();
        }
        void ser_GetECGValueCompleted(object sender, GetECGValueCompletedEventArgs e)
        {
            this.chart.Series[0].ItemsSource = e.Result;
        }

when i run the project, it show "no data to plot".. please help me to resolve this issue