I have a pivot table report in zoho reports (data source : Zoho crm).

I need a column in this pivot report that can perform a calculation "column x - column y", column y being a total of several columns in the same report.

I can see that adding a custom formula column is not available in a pivot report- or at least I have not been able to figure out how to do so.

Is there a solution, please? 

Thank you