private void UpdatePivots()
 {
     Books.Navigate(typeof(Books), lastSelectedIndex - 1);
     Handouts.Navigate(typeof(Handout), lastSelectedIndex - 1);
     TeacherList.Navigate(typeof(Teachers), lastSelectedIndex - 1);
     TestList.Navigate(typeof(Tests), lastSelectedIndex - 1);
     Timings.Navigate(typeof(Timings), lastSelectedIndex - 1);
 }