8.1.2 Other Reserved Keywords

  In  addition to the mandatory keywords defined in §8.1.1, the following keywords may be used to describe the structure of an ASCII table data array. They are optional, but if they appear within an ASCII table extension header, they must be used as defined in this section of this standard.

TSCALn Keywords

This indexed keyword shall be used, along with the TZEROn keyword, when the quantity in field n does not  represent a true physical quantity. The value field shall contain a floating point number representing the coefficient of the linear term in Eq. 8.1, which must be used to compute the true physical value  of the field. The default value for this keyword is 1.0. This keyword may not be used for A-format fields.

TZEROn Keywords

This indexed keyword shall be used, along with the TSCALn keyword, when the quantity in field n does not represent a true  physical quantity. The value field shall contain a floating point number representing the zero point for the true physical value of field n. The default value for this keyword is 0.0. This keyword may not be used for A-format fields.

The transformation equation used to compute a true physical value from the quantity in field n is 

physical_values = TZEROn + TSCALn × field_values.

(8.1)

TNULLn Keywords

The value field for this indexed keyword shall contain the character  string that represents  an undefined value for field n. The string is implicitly blank filled  to the width of the field.

TTYPEn Keywords

The value field for this indexed keyword shall contain a  character string, giving the name of field n. It is recommended that only letters, digits, and underscore  (hexadecimal code 5F, ``_'') be used in the name. String comparisons with the values of TTYPEn keywords should not be case sensitive. The use of identical names for different fields should be avoided.

TUNITn Keywords

The value field shall contain a character string  describing the physical units  in which the quantity in field n, after any application  of TSCALn and TZEROn, is  expressed. Units must follow the prescriptions in §5.3.