code: def _fix_left(self, reading_id, last, start, found_id):
          
  
          accum_delta = 0
          exact = True
          crossed_break = False
  
          if start == 0:
              return None
  
          for curr in self._anchor_points.islice(None, start - 1, reverse=True):
              if curr.uptime is None or last.uptime is None:
                  exact = False
              elif curr.is_break or last.uptime < curr.uptime:
                  exact = False
                  crossed_break = True
              else:
                  accum_delta += last.uptime - curr.uptime
  
              if curr.utc is not None:
                  time_delta = datetime.timedelta(seconds=accum_delta)
                  return UTCAssignment(reading_id, curr.utc + time_delta, found_id, exact, crossed_break)
  
              last = curr
  
          return None
docs: Fix a reading by looking for the nearest anchor point before it.