In each subform, in the footer, place a calculated field that adds up the
Debits or the Credits accordingly.
ex. [SumDebits] and [SumCredits]
Since you'll be referring to these fields from the Tab on the Main form,
you would address the sumDebits as...
(ex. name = [TotalDebits])
Do the same for sumCredits...
(ex. name = [TotalCredits])
Now you can just create a third calculated field with
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