How would you implement crosshair in DDD WPF Charts?

I ended up using DDD as my main charting for WPF. Need to implement crosshair (two lines which follow mouse pointer).

Which particular class in DDD is the best to override?

EDIT : actually I discovered that there is already element which does what I need. Just add this into the Plotter XAML.

<ddd:CursorCoordinateGraph/>

To keep this question for information purpose I am going to answer it myself.

Apparently DDD already has crosshair. To enable this you need to :

<ddd:ChartPlotter>
...            
    <ddd:CursorCoordinateGraph/>
...
</ddd:ChartPlotter>