Sample:
You have 2 accounts A1 and A2
A1=1000 and A2=1500
You create journal adjustment A1 +200 and A2 -200
The result will be:
A1=1200 and A2=1300
If you write ANY logic script in calculations 1200 or 1300 will be used - final values after journal
In your case it's even worse - you have number of values to be aggregated and the script has to calculate this aggregation
Vadim