The following example shows how you can use the Undo method within a control's Change event procedure to force a field named LastName to reset to its original value, if it changed.
Private Sub LastName_Change()
Me!LastName.Undo
End Sub
The next example uses the Undo method to reset all changes to a form before the form is updated.
Private Sub Form_BeforeUpdate(Cancel As Integer)
Me.Undo
End Sub