This part of IEC 60793 establishes uniform requirements for the monitoring of changes in attenuation, thereby assisting in the inspection of fibres and cables for commercial purposes. This standard gives two methods for monitoring the changes in attenuation of optical fibres and cables that occur during mechanical or environmental testing, or both. It provides a monitor in the change of attenuation characteristics arising from optical discontinuity, physical defects and modifications of the attenuation slope: method A: change in attenuation by transmitted power; method B: change in attenuation by backscattering. Methods A and B apply to the monitoring of all categories of the following fibres: class A: multimode fibres; class B: single-mode fibres; class C: single-mode intraconnection fibres. Information common to both measurements is contained in clauses 1 to 10, and information pertaining to each individual method appears in annexes A, and B respectively.