I am trying to figure out how to display a tooltip showing the Y-axis value for a datapoint whenver the mouse is over any part of the particular column.

For example, I have two series in my chart, so each stacked column has two parts.  If I hover the mouse over the lower column in the stack, I would like to display a tooltip that represents the Y axis value for that part of the stack.

I know that I can add a marker, but I only get the tooltip if I hover right over the small circle at the top of the column in the stack.

Can anyone get me pointed in the right direction?

Thanks.