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SECTION 4. HEADERS

an uppercase T or F as the first non-space character in bytes 11 through 80.

4.2.3

Integer Number

If the value is a fixed-format integer, the ASCII representation shall be right-justified in

bytes 11 through 30. An integer consists of a `+' (decimal 43 or hexadecimal 2B) or `-'

(decimal 45 or hexadecimal 2D) sign, followed by one or more contiguous ASCII digits

(decimal 48 to 57 or hexadecimal 30 to 39), with no embedded spaces. The leading

`+' sign is optional. Leading zeros are permitted, but are not significant. The integer

representation shall always be interpreted as a signed, decimal number. This standard

does not limit the range of an integer keyword value, however, software packages that

read or write data according to this standard could be limited in the range of values that

are supported (e.g., to the range that can be represented by a 32-bit or 64-bit signed

binary integer).

A free-format integer value follows the same rules as fixed-format integers except

that the ASCII representation may occur anywhere within bytes 11 through 80.

4.2.4

Real Floating-Point Number

If the value is a fixed-format real floating-point number, the ASCII representation shall

be right-justified in bytes 11 through 30.

A floating-point number is represented by a decimal number followed by an optional

exponent, with no embedded spaces. A decimal number shall consist of a `+' (decimal 43

or hexadecimal 2B) or `­' (decimal 45 or hexadecimal 2D) sign, followed by a sequence

of ASCII digits containing a single decimal point (`.'), representing an integer part

and a fractional part of the floating-point number. The leading `+' sign is optional.

At least one of the integer part or fractional part must be present. If the fractional

part is present, the decimal point must also be present. If only the integer part is

present, the decimal point may be omitted, in which case the floating-point number is

indistinguishable from an integer. The exponent, if present, consists of an exponent

letter followed by an integer. Letters in the exponential form (`E' or `D')  1 shall be

upper case. The full precision of 64-bit values cannot be expressed over the whole range

of values using the fixed-format. This standard does not impose an upper limit on

the number of digits of precision, nor any limit on the range of floating-point keyword

values. Software packages that read or write data according to this standard could be

limited, however, in the range of values and exponents that are supported (e.g., to the

range that can be represented by a 32-bit or 64-bit floating-point number).

1

The `D' exponent form is traditionally used when representing values that have more decimals

of precision or a larger magnitude than can be represented by a single-precision 32-bit floating point

number, but otherwise there is no distinction between `E' or `D'.

FITS Standard