Fibre optic power meters are designed to measure optical power from fibre optic sources as accurately as possible. This capability depends largely on the quality of the calibration process. This International Standard standardizes all of the steps involved in the calibration process: establishing the reference conditions, carrying out the calibration, calculating the uncertainty, and reporting the uncertainty, the reference conditions, and the traceability. It also creates a standardized type of power meter specification, which will make it easier to compare power meters from different vendors.