Formula to show change from previous month

I am sure there is way to do this, I am just not sure how.

Date Customer ATM IP Total ATMDif IPDif
08/01/14 Company 1 250 325 575
08/01/14 Company 2 132 285 417
09/01/14 Company 1 249 333 582 (1) 8
09/01/14 Company 2 130 290 420 (2) 5

This is a running table from month to month. I want to be able to see the change for each customer for both the ATM count, and the IP count.
I need a formula that will look at each count, and show the difference from the prior month. So say in August, customer 1 had 250 clients on ATM and in Sept it was 249. The change is shown there as -1, but I would like a formula to automatically do that. So it will need to look at a previous date, for the same customer, and look at both ATM and IP counts.
Hope that makes sense.

In F2 try this:

Formula:

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It should be able to be dragged down and across.

It assumes all dates are the first of the month. It will return a blank if there was no record the previous month.

I thin that should be sumifS()...
=IFERROR(C2-SUMIFs(C$1:C1,$B$1:$B1,$B2,$A$1:$A1,EDATE($A2,-1)),"")

Originally Posted by FDibbins

I thin that should be sumifS()...
=IFERROR(C2-SUMIFs(C$1:C1,$B$1:$B1,$B2,$A$1:$A1,EDATE($A2,-1)),"")

Thanks Ford.