How to do calculation on sum.
Hi.
I wondered if it was possible to do anything with the built in sum. I was wanting to take 1 sum away from another to get a balance. Or is there a bit of code to sum 2 fields eg credit and debit then subtract one from the other.
Thanks for any pointers.

By built in sum I assume you mean the one at the end of a table column? You can't use this per se (and note it changes depending on any filters you apply to the table).
The formula for the sum of values in a a table is simply "sum('Field')  so in your example above, sum(credit)sum(debit) would give the result you require. Note this this will include ALL credits and debits in a table. 
By built in sum I assume you mean the one at the end of a table column? You can't use this per se (and note it changes depending on any filters you apply to the table).
The formula for the sum of values in a a table is simply "sum('Field')  so in your example above, sum(credit)sum(debit) would give the result you require. Note this this will include ALL credits and debits in a table.