Interactivity

Scale interactivity refers to the ability for the end-user to interact with the scale object. This ability is governed by the Boolean IsInteractive property. When this Boolean value is set to True, the end-user can click on the scale or drag the indicator along the values of its scale.

<telerik:RadRadialGauge Width="200" Height="200" telerik:StyleManager.Theme="Windows8"> 
        <telerik:RadialScale IsInteractive="True"> 
        <telerik:RadialScale.Indicators> 
            <telerik:Needle Name="needle" Value="85" /> 
            <telerik:Pinpoint /> 
            <telerik:Marker telerik:ScaleObject.Location="Outside" 
                            Value="15" /> 
        </telerik:RadialScale.Indicators> 
    </telerik:RadialScale> 
</telerik:RadRadialGauge> 

When end-user click on a scale at an approximate value all indicators move, or snap, to a value on the scale which is closest to where the end-user clicked.

The end-user can click and drag the indicator along the values of its scale.

Using interactivity features of the scale you can create two-way binding between indicator’s value and value of any other control (RadNumericIndicator, for example).

<Grid Margin="20"> 
    <Grid.ColumnDefinitions> 
        <ColumnDefinition Width="Auto" /> 
        <ColumnDefinition Width="Auto" /> 
    </Grid.ColumnDefinitions> 
    <telerik:RadRadialGauge Width="200" Height="200" 
                            HorizontalAlignment="Left" 
                            VerticalAlignment="Top" 
                            telerik:StyleManager.Theme="Windows8"> 
        <telerik:RadialScale Min="0" Max="100" IsInteractive="True"> 
            <telerik:RadialScale.Indicators> 
                <telerik:Marker Name="marker" 
                                telerik:ScaleObject.RelativeHeight="0.1*" 
                                telerik:ScaleObject.Location="OverCenter" 
                                Value="{Binding ElementName=markerValue, Path=Value, Mode=TwoWay}"  /> 
            </telerik:RadialScale.Indicators> 
        </telerik:RadialScale> 
    </telerik:RadRadialGauge> 
    <Grid Grid.Column="1"> 
        <Grid.ColumnDefinitions> 
            <ColumnDefinition Width="Auto" /> 
            <ColumnDefinition Width="Auto" /> 
        </Grid.ColumnDefinitions> 
        <TextBlock>Marker value:</TextBlock> 
        <telerik:RadNumericUpDown Name="markerValue" 
                                    Grid.Column="1" 
                                    VerticalAlignment="Top" 
                                    Width="100" 
                                    Height="21" 
                                    Minimum="0" 
                                    Maximum="100" 
                                    Value="20" 
                                    telerik:StyleManager.Theme="Windows8"/> 
    </Grid> 
</Grid> 

When end-user click on the scale or drag indicator along the scale values the value of the RadNumericIndicator will be changed correspondently.

You should add reference to Telerik.Windows.Controls.Input.dll in order to use the RadNumericIndicator control