(1) are invoice numbers that is used to search in a dataset to the corresponding invoices
in the second control is the invoice number availabe (2) and the credit (3) that has to be applied to the table in an additional column (4). The credit (3) that has to be applied to the table has obviously to be matching the invoice numbers in the table (5).
in other words for invoice (1) found in (2) should (3) be added in column (4) for each record where (1) =(2) = (5)