The best way to do this is to set the record source of the puchase orders subform to the inventory transactions
query instead of the table. I don't think you're going to get what you want (whatever that is) just by messing around with an unbound box. If you set the RS to the Invent. Trans. query and include in that a calculated field for the "Due" column, it will display the "column - column" figure that you are looking for in each record.That's not at all a mistake Md, because the code you wrote was with the OnCurrent event. That's exactly what's suppose to happen.
Personally, I think you are reading way too much into this!! I don't have a lot of time to try and figure out what means what in your database, but if the above solution does result in an answer for you, I think people would be "all ears" regarding an explanation of what your intentions were when setting this up. I personally, wouldn't mind hearing...
*What exactly the "due" column is for.
*And what role you want that column to play in the "live" computation of "on-hand" inventory or tracking receipts.
Just by browsing through, I can see the typical setup for inventory tracking based on purchase orders, and the differences in receipts/shipments. More explanation, even in-depth stuff is welcome, at least from me...