Simple Forms Question

[hapajapa0218]

I would like to have a form that displays a single record at a time, and when the user modifies any field then clicks the save button, record the modification to a file on disk.. I currently am using this:

Private Sub txt_homephone_BeforeUpdate(Cancel As Integer)

DoCmd.OutputTo acOutputForm, Main_Form, acFormatTXT, "a:Output.txt", True

End Sub

But each time it prints all records to the file.. all I want is the record (or even field) that was modified.

Thanks.