code: def compensate_system_time_change(self, difference):  # pragma: no cover,
          # not with unit tests
          
          # We only need to change some value
          for prop in ('last_notification', 'last_state_change', 'last_hard_state_change'):
              val = getattr(self, prop)  # current value
              # Do not go below 1970 :)
              val = max(0, val + difference)  # diff may be negative
              setattr(self, prop, val)
docs: If a system time change occurs we have to update
          properties time related to reflect change
  
          :param difference: difference between new time and old time
          :type difference:
          :return: None