Fw.d (Fixed Floating Editing)

  On input, F transfers "w" characters from the external field and
  assigns them, as a real value, to the corresponding I/O list
  element (which must be real data type).  If the first nonblank
  character of the external field is a minus sign, the field is
  treated as a negative value.  If the first nonblank character is a
  plus sign or if no sign appears in the field, the field is treated
  as a positive value.

  If the field contains neither a decimal point nor an exponent, it
  is treated as a real number of "w" digits, in which the rightmost
  "d" digits are to the right of the decimal point, with leading
  zeros assumed if necessary.  If the field contains an explicit
  decimal point, the location of the decimal point overrides the
  location specified by the field descriptor.  If the field contains
  an exponent, that exponent is used to establish the magnitude of
  the value before it is assigned to the list element.

  On output, F transfers the value of the corresponding I/O list
  element, rounded to "d" decimal positions and right-justified, to
  an external field that is "w" characters long.  If the value does
  not fill the field, leading spaces are inserted; if the value is
  too large for the field, the entire field is filled with asterisks.

  The term "w" must be large enough to include all of the following:
  a minus sign (when necessary) or a plus sign (if SP editing is in
  effect), at least one digit to the left of the decimal point, a
  decimal point, and "d" digits to the right of the decimal.

  Therefore, "w" must be greater than or equal to "d"+3.