code: def _getAvailableInstrumentsDisplayList(self):
          
          bsc = getToolByName(self, 'bika_setup_catalog')
          items = [(i.UID, i.Title)
                   for i in bsc(portal_type='Instrument',
                                is_active=True)]
          items.sort(lambda x, y: cmp(x[1], y[1]))
          return DisplayList(list(items))
docs: Returns a DisplayList with the available Instruments
              registered in Bika-Setup. Only active Instruments are
              fetched. Used to fill the Instruments MultiSelectionWidget