A better way of calculating the dollar value of sales invoices

I wrote the other day about code to calculate the dollar value of sales invoices. I had written code that iterated by means of a cursor over the lines of an invoice and calculated the dollar value of each line, then summing these values. I was sure that there was a better way of doing this but I hadn't managed to find this better way. While I was describing the problem, I saw the quick way of getting the dollar value, using values in the connected transaction. This is yet another case of rubber duck debugging: describing the problem in words leads to a solution. Here is the code that is stored as a trigger in the 'func' form.

/***********************************************************
TEST_CNVINV2DOLLAR - Convert an invoice's total to dollars
11/11/23: New, much simpler version that doesn't require a cursor
and so can be used multiple times in a container procedure.
SUB 6200 -
Input: :IV
Output: :QP
************************************************************/
SUB 6200;
:VAT62 = :SUM62 = :EXCHANGE62 = :QP = 0.0;
:TMP62 = 0E9;
:DEBIT62 = '\0';
SELECT INVOICES.VAT, INVOICES.DEBIT, FNCTRANS.SUM2,
FNCTRANS.EXCHANGE2
INTO :VAT62, :DEBIT62, :SUM62, :EXCHANGE62
FROM INVOICES, FNCTRANS
WHERE INVOICES.FNCTRANS = FNCTRANS.FNCTRANS
AND INVOICES.IV = :IV;
:TMP62 = :VAT62 / :EXCHANGE62;
:QP = (:DEBIT62 = 'C' ? -1 : 1) * (:SUM62 - :TMP62);
RETURN;

Short and simple.