This file must be loaded into the user's program by a call to
      the FURNSH subroutine
 
            CALL FURNSH( 'this_file_name' )
 
      in order to use the SPICELIB SCLK family of subroutines to
      convert MGS spacecraft on-board clock to ET and vice versa and
      to use MGS frames defined below as reference frames for
      geometric quantities being returned by high-level SPK and
      CK subroutines.
 
 
   References
   -----------------------------------------------
 
      1. SCLK Require