Combo Box Value not Shown

I have a combo box on a form which using a 'not in' qry.

The combo box has two columns, ID and Serial# (which are
in the same table)

ID is hidden in combo box (width set to 0")

ID is the bound column.

The not in query will not allow to select serial# (ID) if
that Serial# exists in the table the form is bound to.

Hence Once a serial# has been selected it may not exist in
another record (no duplicates) and is no longer available
in the list.

The problem I am having is since the Serial# is removed in
the list you can longer see that you have selected it in
the current record.

Is there a way I may fix this. I would rather not have to
create a seperate list or text box to show the selected
value. I would just like it to remain in the combo box
for that record.

Is this happening becuase the bound column is not visible?

bound column (ID) is of no use to the users. Serial# is
the only thing they will recognize.

Help is greatly appreciated.

Thank You,
Tim J