ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

International Standard ISO 13443 was prepared by Technical Committee ISO/TC 193, Natural gas.

Annexes A and C form an integral part of this International Standard. Annexes B, D, E and F are for information only.

The multiplicity of so-called "standard reference conditions" of temperature, pressure and humidity (state of saturation) used in the measurement of natural-gas quality and quantity can cause much confusion. Failure to take unrecognized differences of reference conditions into account can have serious consequences in, for example, custody transfer applications. Often enough, even an experienced gas engineer may not recognize the potential for error, as the units of measurement usually employ identical terminology, irrespective of differences in the reference conditions. All of the ambiguity and its undesirable consequences may easily be removed by the adoption of a single standardized set of reference conditions. The set chosen in this International Standard will be known as the ISO standard reference conditions.