Track values of current mouse cursor X position.
Can be seen here: 
http://www.google.com/finance?q=INDEXDJX:.DJI,INDEXSP:.INX,INDEXNASDAQ:.IXIC
and here:
http://people.iola.dk/olau/flot/examples/tracking.html

REASON FOR DECLINATION
This is supported out-of-the-box by the new RadChartView (TrackBallBehavior & CrosshairBehavior).