IEC 61280-4-4:2017(E) provides uniform methods of measuring polarization mode dispersion (PMD) of single-mode installed links. An installed link is the optical path between transmitter and receiver, or a portion of that optical path. These measurements can be used to assess the suitability of a given link for high bit rate applications, or to provide insight on the relationships of various related transmission attributes. This document focuses on the measurement methods and requirements for measuring long lengths of installed cabling that can also include other optical elements, such as splices, connectors, amplifiers, chromatic dispersion compensating modules, dense wavelength division multiplexing or multiplexer (DWDM) components, multiplexers, wavelength selective switches, re-configurable optical add drop multiplexer (ROADMS). This document focuses on the apparatus, procedures, and calculations needed to complete measurements. IEC TR 61282-9 explains the theory behind the test methods. This second edition cancels and replaces the first edition published in 2006. This second edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:- theory is removed and replaced with a reference to IEC TR 61282-9;- a new method, wavelength scanning OTDR and SOP analysis (WSOSA), is added as Annex G;- a brief description of each method is added to Clause 5;- Methods E and F are converted to informative Annexes E and F;- a new Clause (6) on measurement configurations is added;- a new Clause (7) on measurement considerations is added;- Clause 10 on procedure is expanded;- several of the apparatus diagrams are improved;- several clarifications about what is measured and what is calculated have been made in Annex H.Keywords: Polarization mode dispersion (PMD), single-mode installed links