18.2.4 HFLOAT Floating-Point Number Format
              (H_floating)-VAX BASIC Only
  In VAX BASIC, an H_floating floating-point number is 16
  contiguous bytes, starting on an arbitrary byte boundary. The
  H_floating format combines a large range with extensive
  precision but requires twice the amount of storage of double
  and G_floating numbers. The bits are labeled from the right,
  0 to 127. The form of an H_floating number is sign mag-
  nitude with bit 15 the sign bit, bits 14 to 0 an excess -16384
  binary exponent, and bits 127 to 16 a normalized 113-bit
  fraction with the redundant most significant fraction bit not
  represented.

  Within the fraction, bits increase in significance from 112 to
  127, 96 to 111, 80 to 95, 64 to 79, 48 to 63, 32 to 47, and 16 to
  31. The 15-bit exponent field encodes the values 0 through
  32767.

  An exponent value of 0 together with a sign bit of 0 indicates
  the H_floating number has a value of 0. Exponent values
  from 1 to 32767 indicate true binary exponents from -16383
  to 16383. The value of an H_floating number is in the ap-
  proximate range .84
                                *

                                    10

                                      4932
                                            to .59
                                                    *

                                                        10

                                                          4932
                                                                . The precision
  of an H_floating number is approximately one part in 2

                                                                                  112
  (approximately 33 decimal digits).