Retrieve a range chart through macro

Hello,

I am trying to add a new series in a graph through macro.

Range of the new series is similar to the other series already plotted in the graph.

Eg. range of series 1: A5:A20 & B5:B20
and range of the new series will be: A5:A20 & C5:C20

The problem is range of the series 1 is dynamic and hence I need to retrieve the range in the macro and then make necesarry changes and assign to the new series.
I am able to retrieve only the values but not the range (A5:A20 & B5:B20).

Does anyone know how to retrieve the range?

Thanks