VMS Help FORTRAN, /DEBUG, SYMBOLS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Controls whether the debugger receives local symbol definitions for
  user-defined variables, arrays, (including dimension information),
  structures, PARAMETER constants, and labels of executable
  statements.

  Unless /DEBUG=PARAMETERS=ALL is in effect, only those PARAMETER
  constants actually used in the program unit are made known to the
  debugger.