Finding On an Unstored Calculation field

[Jeremy English]

I have 2 tables, Contacts and then lineitems, with a number field in lineitems called 'Due'. In Contacts I have a portal showing the lineitems, with an unstored calculation field that is the sum (Due).

I want to find all the contacts for whom money is due, ie Due >0 but this is slow over a large set of data. I was wondering if I could make a portal showing all people who owe money, but this does not work properly. I have tried duplicating the Sum (Due) field in Contacts as an auto-enter calc number field, but this does not update. What is the best method to do this or how do I solve this problem in FileMaker 7?

thank you!