code: def on_prev_button(self, event):
          
          if 'saved' not in self.Data[self.s]['pars'] or self.Data[self.s]['pars']['saved'] != True:
              # check preferences
              if self.auto_save.GetValue():
                  self.on_save_interpretation_button(None)
              else:
                  del self.Data[self.s]['pars']
                  self.Data[self.s]['pars'] = {}
                  self.Data[self.s]['pars']['lab_dc_field'] = self.Data[self.s]['lab_dc_field']
                  self.Data[self.s]['pars']['er_specimen_name'] = self.Data[self.s]['er_specimen_name']
                  self.Data[self.s]['pars']['er_sample_name'] = self.Data[self.s]['er_sample_name']
                  # return to last saved interpretation if exist
                  if 'er_specimen_name' in list(self.last_saved_pars.keys()) and self.last_saved_pars['er_specimen_name'] == self.s:
                      for key in list(self.last_saved_pars.keys()):
                          self.Data[self.s]['pars'][key] = self.last_saved_pars[key]
                      self.last_saved_pars = {}
  
          index = self.specimens.index(self.s)
          if index == 0:
              index = len(self.specimens)
          index -= 1
          self.s = self.specimens[index]
          self.specimens_box.SetStringSelection(self.s)
          self.update_selection()
docs: update figures and text when a previous button is selected