As far as I know, our indicators do not support conditionals which are easily expressed in a spreadsheet, for example like this:
Another issue is how to combine data from different periods - say opening balance of the month should automatically be closing balance from last month - so you would either have to copy the value, or just display the closing balance.
Maybe we could also build up a repository of how-tos for more advanced forms, as part of the documentation and/or as cookbook recipies in an online repository such as this one:
Dept. of Informatics, University of Oslo