sl4 toolkit图表控件显示双y轴

下面是页面代码

<UserControl xmlns:toolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit"  x:Class="SilverlightApplication2.MainPage"
    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"
    mc:Ignorable="d"
               xmlns:local="clr-namespace:SilverlightApplication2"
    d:DesignHeight="300" d:DesignWidth="400" >

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.Resources>
            <local:EngineMeasurementCollection x:Key="EngineMeasurementCollection"/>
        </Grid.Resources>
        <toolkit:Chart>
            <!-- Power curve  -->
            <toolkit:LineSeries
                            Title="Power"
                           ItemsSource="{StaticResource EngineMeasurementCollection}"
                            IndependentValueBinding="{Binding Speed}"
                            DependentValueBinding="{Binding Power}">
                <!--MarkerWidth="5"
                            MarkerHeight="5"-->
                <!-- Vertical axis for power curve  Orientation="Vertical"-->
                <toolkit:LineSeries.DependentRangeAxis>

                    <toolkit:LinearAxis
                         
                                     Orientation="y"
                                    Title="Power (hp)"
                                    Minimum="0"
                                    Maximum="250"
                                    Interval="50"
                                    ShowGridLines="True"/>
                </toolkit:LineSeries.DependentRangeAxis>
            </toolkit:LineSeries>
            <toolkit:ColumnSeries   Title="Power"
                           ItemsSource="{StaticResource EngineMeasurementCollection}"
                            IndependentValueBinding="{Binding Speed}"
                            DependentValueBinding="{Binding Power}">
                <toolkit:ColumnSeries.DependentRangeAxis>
                    <toolkit:LinearAxis    Orientation="y"
                                    Title="Power (hp)"
                                    Minimum="0"
                                    Maximum="250"
                                    Interval="50"
                                    ShowGridLines="True"></toolkit:LinearAxis>
                </toolkit:ColumnSeries.DependentRangeAxis>
            </toolkit:ColumnSeries>
            <!-- Torque curve  -->
            <toolkit:LineSeries
                            Title="Torque"
                           ItemsSource="{StaticResource EngineMeasurementCollection}"
                            IndependentValueBinding="{Binding Speed}"
                            DependentValueBinding="{Binding Torque}">
                <!--MarkerWidth="5"-->
                <!--MarkerHeight="5"-->
                <!-- Vertical axis for torque curve  Orientation="Vertical"-->
                <toolkit:LineSeries.DependentRangeAxis>
                    <toolkit:LinearAxis
                                   Orientation="Y"
                                    Title="Torque (lb-ft)"
                                    Minimum="50"
                                    Maximum="300"
                                    Interval="50"/>
                </toolkit:LineSeries.DependentRangeAxis>
            </toolkit:LineSeries>
            <toolkit:Chart.Axes>
                <!-- Shared horizontal axis Orientation="Horizontal"-->
                <toolkit:LinearAxis
                                Orientation="X"
                                Title="Speed (rpm)"
                                Interval="1000"
                                ShowGridLines="True"/>
            </toolkit:Chart.Axes>
        </toolkit:Chart>
    </Grid>
</UserControl>