The report is to be updated each day (weekends excluded) with that day's report of invoices.  An invoice number may appear on one report or on multiple reports.  The calculated field "Unique invoice number" is used simply to count distinct invoice number per supplier number.

I need to calculate the difference in COUNTD of the calculated field "Unique invoice number" and have it display in the dashboard (see attached) depending on the date filtered (there is an action filter applied to the line graph).  Ideally, I will also be able to calculate the difference for the total and be able to filter by supplier number.

For example, if the date September 18 was selected, the "Inflow/outflow" calculation would equal -291 because the count for Sep 18 is 291 less than the count for Sep 15.  I think this would be described as a line-level calculation?  Maybe there is an easier way to achieve the minimal result without using a calculated field?  Any assistance would be greatly appreciated.