This will be a short post, just to explain quickly how the Calculation of FX Differences works inside of SAP BPC.
We can have the following definition of Currency Translation Rules to calculate the FX Differences Movements in Opening Balance to take in consideration the changes on the Exchange Rates of each Company Currency:
In the following picture, you can see how that calculation will work in our SAP BPC system:
After that calculation, we can use a Business Rule to reclassify all differences and send all of them to a unique dedicated account for Exchange differences.
If you need further information about scenarios within BPC, do not hesitate to contact me under firstname.lastname@example.org