That seems to confirm my impression... the value of STM is solely dependent
on the value of [NT]. Therefore, you do not need to store STM, since
knowing [NT] will suffice.
You could add code to the AfterUpdate event of [NT] that would DISPLAY a
value for STM, but you would not need to store the STM value. In fact, if
you DID store the STM value, your data integrity would be at risk, since it
would be (at least theoretically) possible that someone could change one or
the other of these two fields and not know or remember to update the other.
If you add an upbound checkbox control to your form (e.g., chkSTM), and have
a control bound to your [NT] field (e.g., txtNT), then your code would look
If Me!txtNT = 6 Then
Me!chkSTM = True
Me!chkSTM = False
Microsoft Office/Access MVP