Establishes preferred measurement principles and practices to assure that meaningful data describing the optical loss performance of installed cable plants can be obtained.It is not intended for component testing, it does not define those elements of an installation that need to be measured. This procedure is a specific test associated with IEC 61281-1. This procedure can be used to measure the optical loss between any two passively connected points, including end terminations, of a multimode optical fibre cable plant.