Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
Standard energy measurement of natural gas
ISO 15971 is an ISO standard for calorific value measurement of natural gas and its substitutes. The methods it covered does not involve gas composition determination and the related calculations.
The standard includes the operation of instruments that are used in the measurements and the guidelines in selecting and assessing, as well as the installation and the operation of such instruments.