How to position a tooltip in WPF

The following code snippet adds and positions a tooltip to an ellipse.

 <Ellipse Height="25" Width="50" 
Fill="Gray"
HorizontalAlignment="Left"
ToolTipService.InitialShowDelay="1000"
ToolTipService.ShowDuration="7000"
ToolTipService.BetweenShowDelay="2000">
<Ellipse.ToolTip>
<ToolTip Placement="Right"
PlacementRectangle="50,0,0,0"
HorizontalOffset="10"
VerticalOffset="20"
HasDropShadow="false"
Opened="whenToolTipOpens"
Closed="whenToolTipCloses"
>
<BulletDecorator>
<BulletDecorator.Bullet>
<Ellipse Height="10" Width="20" Fill="Blue"/>
</BulletDecorator.Bullet>
<TextBlock>Uses the ToolTip Class</TextBlock>
</BulletDecorator>
</ToolTip>
</Ellipse.ToolTip>
</Ellipse>