VMS Help SORT, Output File Qualifiers, /INDEXED_SEQUENTIAL, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  $ CREATE/FDL=NEW.FDL AVERAGE.DAT
  $ SORT/KEY=(POS:1,SIZ:80) DATA.DAT,STATS.DAT -
  _$ AVERAGE.DAT/INDEXED_SEQUENTIAL/OVERLAY

      The CREATE/FDL command creates the empty file AVERAGE.DAT. The
      SORT command specifies that the output file have an indexed-
      sequential organization and be written to the empty file
      AVERAGE.DAT.