Serial number in Crosstab

Hi guys,

I have a crosstab that shows sales by a Parent, Territory and Product.

I need to show a serial number that represents the rank of the sales, sales are sorted in descendent way.

How can I add that serial number in the crosstab?

I have tried functions like CurrentFieldValue and CurrentRowIndex but I get errors for both;

For CurrentFieldValue it seems like it does only work on formatting fields.

For CurrentRowIndex, I get "This function can be used only within the context of a value grid"

Any help would be appreciated!