Section 10,18: F

 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.