Okay, let me try the second path. I have a form 'NCMR' with all fields bound to table 'NCMRTable'. I added an unbound text box 'ApprSig' and named its Control Source as:
=DLookUp("[ApprSig]","ApprTable","[ApprCode] =" & [Forms]![NCMR]!ApprNumber).
This DLookup statement successfully updates the 'ProdApprSig' field with the appropriate text from the table 'ApprTable', which contains 2 fields, 'ApprCode' and 'ApprSig'.
After the 'ApprSig' is updated on the form 'NCMR', I need to either hide the 'ApprCode' field on the form or otherwise obscure the value entered, since the 'ApprCode' is a unique passcode.
My first thought was to run a query at this point on the 'ApprTable' fields; however, I couldn't get it to update the 'NCMR' form 'ApprSig' field.
All I really want is for the approver to enter his passcode so an electronic signature can be completed on the form 'NCMR' -- without revealing the passcode to anyone else updating the same form.