Please clarify what "doesn't work."  Also, "Recordset" does not work for reports the way it does for forms, so you need another way to do this.  You can obtain the previous and current field values simply with the code below (see picture below).  Declare currentfieldvalue and previousfieldvalue as global variables.  Every time the Detail event runs, it moves to the next record automatically.  At the start of the Detail event, assign the field value to currentfieldvalue.  At the end of the Detail event, assign the field value to previousfieldvalue.  The next time the Detail event runs, previousfieldvalue will have the last record's field value, allowing you to compare the previous and current values, and take action accordingly.

I changed the code. I try to use oldvalue property. I think this is a better method:

Private Sub Form_AfterUpdate()

  
    If Me!BufferType.OldValue <> Me!BufferType.Value Then
        MsgBox "The value has changed after the update.", vbInformation
    End If
    
End Sub

I tried also on controls AfterUpdate. Nothing happens. The MsgBox doesn't pop up.

Any idea!

Your code above is for forms.  Are we still dealing with reports here, like you said in your first post?  Oldvalue applies to user entries on a form, and has nothing to do with reports.

This one was for a form.