Hi,
If your requirement is something like this you can use below formula-
| Document NO | Item NO | Material NO | Issue Date | Amount |
| 123000 | 10 | XYZ1 | 21.06.2014 | 190 |
| 123000 | 10 | XYZ1 | 23.06.2014 | -190 |
| 123001 | 10 | XYZ1 | 24.06.2014 | 100 |
| 123001 | 10 | XYZ1 | 25.06.2014 | 300 |
AmountAfter=If (Sum([Amount]) In([Document NO];[Item NO]))=0 Then Sum([Amount]) In([Document NO];[Item NO]) Else [Amount]
If your requirement is not like above then pls share some screenshot how you want to display the output.
~Anuj