How to add data to Pivot graph?

Hi,
I am creating a pivot table.
Then, outside the Pivot table I am doing calculation.
Then I want to use the pivot graph option, and to add the calculation resoults to the pivot graph.

In the "select data source" menu, the "Add" is gray. (Excel 2007)
How can I do it?

Best regards,

Oops,
I post my question in the workshop by mistake...
Should be in the Excel General.
How do I move it there?
Tnx.