Okay, lets continue with this code.  When I sent it to you, I assumed you
were sure that either County or City would be Null.  I would run the code in
debug and see what the values of the County and City are when it hits the
Select statement.  I also see a possible bug.  There is no check to see if
they are both Null.  

Also, I don't understand the need for a default of 1.  What is the purpose
of that requirement?

Hi, Tom.

Yes.  Your code is attempting to change the value typed into the text box
before the bound text box is updated.  Your code should be attempting to
change the value in another control, not the same control.

Use the Case Else statement as the default value.  Your current Case Else
value is probably only intended to apply if the population is over 200,000,
but that 3.5 multiplier will be applied as the default for all cases not
covered, which isn't what you want.  To get the effects you want, I'd
recommend something like the following VBA code:

' * * * * Start Code * * * *

Private Sub txtSomething_AfterUpdate()

   On Error GoTo ErrHandler
   
   Dim Result As Single    
 
   Select Case Nz(Me!CountyPopulation.Value, Me!CityPopulation.Value)
        Case 1 To 20000
            Result = 1
        Case 20001 To 40000
            Result = 1.5
        Case 40001 To 100000
            Result = 2.5
        Case 100001 To 200000
           Result = 3
        Case Is > 200000
           Result = 3.5
        Case Else
            Result = 1
    End Select
   
   Me!PopulationBracket.Value = Result
     
   Exit Sub
   
ErrHandler:
   
   MsgBox "Error in txtSomething_AfterUpdate( ) in " & vbCrLf & _
           Me.Name & " form." & vbCrLf & _
           "Error #" & Err.Number & vbCrLf & Err.Description
   Err.Clear
   
End Sub

' * * * * End Code * * * *

... where PopulationBracket is the name of the bound text box that holds the
assigned billing multiple for the current population, and txtSomething is the
name of the text box that is being updated with a value during the course of
filling in the form.  With the above logic, if both the county and city
populations have values (boo boos do happen), then the county population will
be used for the billing multiplier.

It might be better to have a command button that the user can click on to
calculate the billing multiplier, but if users tend to forget steps, then the
code should be doing as much automation as possible and an AfterUpdate( )
event is fine for this.

HTH.

Gunny

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