FUNCTION scan_grib_messize, num, recstart
;
  nrec =  n_elements(recstart)
  messize = lonarr(nrec)
;
  FOR i = 0L,nrec-1 DO BEGIN
    offset = recstart[i]
    a = assoc(num, bytarr(1, /nozero), offset+4)
    messize[i] = bit2int([binary(a[0]), binary(a[1]), binary(a[2])])
  ENDFOR
;
  RETURN, messize
END