IEC 62180-4-2:2024 is applicable to the measurements of attenuation and optical return loss of an installed optical fibre cabling plant using single-mode fibre. This cabling plant can include single-mode optical fibres, connectors, adapters, splices, and other passive devices. It is also called. ity check. This type of testing is the most accurate testing available and is the most accurate characterization of the fiber optic system's apability. Testing with. Beginning with software release 1. the reflection above the fiber backscatter level, relative to the source pulse, is called reflectance.