What you describe does not "add up" in more ways than one. I think you need to describe your design in more detail.
If cost 1 and Cost 2 are number fields defined in the layout's (or a portal's) table, then Cost1 + Cost2 should compute the sum of those two fields. But what you describe is more typical of incorrectly implemented summary fields in stead of fields of type calculation.
Thanks for your response, sorry if I didn't explain things well:
Yes, both Cost1 & Cost2 are number fields. On each of these fields, I set the column to show "Trailing Subtotals". The correct totals do appear at the bottom of their respective columns.
I thought by adding a third field (Grand Total) I would be able to display the sum of Cost1 + Cost2 at the bottom of the new column.
This works but unfortunately the sum (cost1+cost2) appears in every record of the table!
sum ( cost1 + Cost 2 ) is not the correct syntax for computing the total of Cost1, Cost2. Is that the exact form of your calculation?
Instead of trying to do this with table view, I would use List view where I can add specific layout parts for totals and subtotals to my layout.Creating Filemaker Pro summary reports--Tutorial
Many thanks for your advice, will give this a try.