How to add dynamic value in tooltip-formula?

Hi,

I have a report with an XY Line chart. I want to add a formula so that whenever I hover over that data point,
the tooltip shows the value of that particular datapoint.

I have tried playing around with the "tooltip-formula" property under Values Tab when you click on chart properties
but no success.

I can add : =[Column_Name]
But this sets the column name static with the first value from the data set for all data points.

Thanks
A