The one-cord method is used for permanent link testing and calls for the launch cord to be attached directly to the power meter for the reference and assumes the power meter has an interchangeable adapter. It is used when the cabling under test has adapters or sockets on both ends of. For every fiber optic cable plant, you need to test for continuity and polarity, end-to-end insertion loss and then troubleshoot any problems. The OTDR trace can be used for cable acceptance, splice and connector loss, documentation, troubleshooting, fault location, optical return loss, and to measure the length of PM cannot.