Crossing point in a Graph

[#1]

Hi I have a  graph with two dimensions YearmMonth and CustomerSupplier, I also have an expressión with the folllowing formula:

Sum( {<[DocumentDate]={'<=$(=Date(vFFF)) >=$(=Date(vFIF))'} , CustomerSupplier={'Customer'} >} [InvoiceRemainingAmount]) + 
Sum( {<[DocumentDate]={'<=$(=Date(vFFF)) >=$(=Date(vFIF))'} , CustomerSupplier={'Supplier'} >} [InvoiceRemainingAmount]) *-1

The graph displays like this:

What I would like to know is the first date where the Customer Amount is larger than the Supplier's. I doný know if this is possible. Does anybody have an idea? Thanks in advance for you help and feedback.