VMS Help PASCAL, Data Types, Real, DOUBLE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The  DOUBLE  type  denotes  double-precision  real  values.   To
  indicate a double-precision real number, you must include a real
  number or an integer, the  letter  D  (or  d),  and  an  integer
  exponent with its minus sign or optional plus sign.  The largest
  DOUBLE value is denoted by MAXDOUBLE.  The smallest DOUBLE value
  is  denoted  by  MINDOUBLE.   EPSDOUBLE  denotes  the  result of
  subtracting 1.0d0 from the smallest DOUBLE value that is greater
  than 1.0d0.

  Example:  0D0
            4.371528665D-3

  On  OpenVMS  VAX  systems,  DOUBLE  exists   in   two   formats:
  D_Floating  and  G_Floating.   On  OpenVMS Alpha systems, DOUBLE
  exists in  three  formats:   D_Floating,  G_Floating,  and  IEEE
  T_Floating.

  To specify a format, you can use either the FLOAT  attribute  or
  the  /FLOAT command line qualifier.  On OpenVMS VAX systems, the
  default format is D_Floating.  On  OpenVMS  Alpha  systems,  the
  default format is G_Floating.