Hi abbey,

a simple solution would be this small procedure in the Workbook_WindowActivate sub.

Advantage: From opening the workbook till closing - always 2 windows of the same file are open.

Disadvantage: File can only be closed by menu File->close
Flipping of the window if you want to close one
But a thing this one can be achieved.

best regards

TheOnly

Code:
Private Sub Workbook_WindowActivate(ByVal Wn As Window)
 
  
   With ThisWorkbook
   
      If InStr(1, Wn.Caption, "xls:") = 0 Then
               .NewWindow
               .Windows.Arrange xlArrangeStyleHorizontal
      End If
   
   End With
End Sub