This part of IEC 60793 establishes uniform requirements for measuring the length and elongation of optical fibre (typically within cable). The length of an optical fibre is one of the most fundamental values and shall be known for the evaluation of transmission characteristics such as losses and bandwidths. In addition, informative Annex F has been added to determine the tensile strain applied to a fibre. It uses Brillouin reflectometry (BOTDR) or so-called Brillouin analysis (BOTDA), which are single-sided and double-sided methods respectively.