I want to show a datapoint marker, showing the data point values, when the mouse hovers over the plot in a 2D chart.  I only want to see the marker for the value that the mouse is over and when the mouse moves off the data point the marker goes away.  So as the user moves the mouse over a 2D plot of data a single marker appears at the data point displaying the data values at the current mouse location.  I have seen the code for doing a hit test off the mouse.  But How do I show a single marker for the data point that is hit?

thanks.