VMS Help FORTRAN, Format Specifiers, P, G field descriptor  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  nPGw.d

  On output, the effect for the G field descriptor is suspended if
  the magnitude of the data to be output is within the effective
  range of the descriptor (because the G field descriptor supplies
  its own scaling function).  It functions as an E field descriptor
  if the magnitude of the data is outside its range.  In this case,
  the scale factor has the same effect as for the E field descriptor.