Crystal Reports sumarize with a condition on a formula calculation

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Hi There,hope the subject gives somewhat of a clue.
I haven't done much Crystal Report development over the last years so please be patient with me. I just ended up in a project where I need to build a couple reports as well. All was well until I needed to just built this sum.
Did a lot of google search and always ended up on this site. So here it goes.

I have a report that I created against an SAP ECC 6 environment. I have a column where the results are created utilizing a formula and a record restriction. Another column that delivers different results effects if I have more or less rows returned in the report. If I have more results my initial column repeats its result (if I only have 1 result returned by its formula) for each created row. 
I want to create a formula that only adds the results of my formula column if its results differ from each other, otherwise use just one value as the sum. 
I guess the most important aspects are:

I  have created 5 groups due to the report design.
Group 1 : Project number
Group 2 : Project location
Group 3: Project Manager
Group 4: WBS
Group 5: PO#

Group 1 - Group 3 are in Group headers 1-3 and build one section.
Below those 3 groups I can have multiple WBS Each WBS has at least 1 PO# sometimes multiple.
How I need the calculation to work is the following:
WBS . . . . . . .
PO#          Date     Vendor       PO Amount     Received
1               1.1.1      A              120                  60
1                1.1.1      A             120                  50    
1                1.1.1     A               120                 10

Additionally possible
1                1.1.1     A               50                   50

Also possible (for same WBS)
2                 1.2.1    B                70                   40
2                  1.2.1   B                70                   30
The PO Amount was calculated with a formula and a record selection. What I need is the sum of column PO Amount. But only sum different amounts like in the example above: 120+50 and possibly +70. If amounts are repeated ignore and only use one as the sum. 
Any advice how I do this? Thanks Stephan