How to implement Touch based rotation with windows 8 app using C# and XAML

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=> How to implement Touch based rotation with windows 8 app using C# and XAML

I have mine windows 8 analog clock app that perform Touchable task to move minutes and hour angle by single touch ,but it could not work properly. it seems to be did not find angle correctly . I had worked on Manupulation delta events of clock needle ( i.e Line ) . When I moved needles forward than 1st time it goes some points backward. I don't know how this is happning. Please anyone can let me know how can I solve this issue. Ma complete code is below.

XAML Code is :-

<Line Name="Hours" PointerEntered="ShowHand" PointerExited="ShowArrow" HorizontalAlignment="Center" VerticalAlignment="Center" X1="0" Y1="0" X2="0" Y2="-70" Stroke="Wheat" Margin="1,0,0,0" StrokeThickness="3" Grid.RowSpan="8" ManipulationDelta=" HourRight_ManipulationDelta" ManipulationMode="TranslateInertia,TranslateX,TranslateY">
            <Line.RenderTransform>
                <RotateTransform x:Name="HoursTransform" CenterX="0" CenterY="0" Angle="{Binding HourHandAngle}" />
            </Line.RenderTransform>
        </Line>

.cs Code is:-

private void HourRight_ManipulationDelta(object sender, ManipulationDeltaRoutedEventArgs e)
    {
        var x = HoursTransform.CenterX - e.Position.X;
        var y = HoursTransform.CenterY - e.Position.Y;

        var angle = Math.Atan(y / x);
        var deltaAngle = Math.Atan((e.Delta.Translation.Y - y) / (x - e.Delta.Translation.X));

        this.HoursTransform.Angle += angle - deltaAngle;
    }

Kinds Regards in advance