READ

        [MRTCAL\]READ   [FileName|FileNum|FIRST|LAST|NEXT|PREV]  [/FILENAME]
    [/SUBSCAN Isub]
        [MRTCAL\]READ ZERO

    Load a file in the Mrtcal buffers:
      - the 4 first HDU in the  IMBFITS  file  (namely  Primary,  IMBF-scan,
        IMBF-frontend and IMBF-backend), and then read
      - the 3 HDU IMBFITS-backendXXX, IMBFITS-antenna and IMBFITS-subreflec-
        tor (this latter not implemented) for the subscan number  Isub  (de-
        fault 1)
      - the on-track part of the DATA column of the HDU IMBFITS-backendXXX
          is read (take care that it may be large).

    Without  argument,  the command will try to read again the current file-
    name.  Else the command argument can be either
      - the file name when the /FILENAME option is present,
      - the file number (and optionally its version) in the Input index, of
          the form Num (or Num.Ver),
      - the FIRST|LAST file in Current indeX,
      - the NEXT|PREVIOUS file in Current indeX, considered from previous
          call to the command.

    The reference file (for NEXT or PREVIOUS) in Current indeX is  reset  by
    the  command MFIND. READ ZERO also reset the reference file and does not
    read any file.