code: def backend_calibration(self, backend='ibmqx4', hub=None, access_token=None, user_id=None):
          
          if access_token:
              self.req.credential.set_token(access_token)
          if user_id:
              self.req.credential.set_user_id(user_id)
          if not self.check_credentials():
              raise CredentialsError('credentials invalid')
  
          backend_type = self._check_backend(backend, 'calibration')
  
          if not backend_type:
              raise BadBackendError(backend)
  
          if backend_type in self.__names_backend_simulator:
              ret = {}
              return ret
  
          url = get_backend_stats_url(self.config, hub, backend_type)
  
          ret = self.req.get(url + '/calibration')
          if not bool(ret):
            ret = {}
          else:
            ret["backend"] = backend_type
          return ret
docs: Get the calibration of a real chip