This part of IEC 60793 establishes uniform requirements for measuring the attenuation of optical fibre@ thereby assisting in the inspection of fibres and cables for commercial purposes. Four methods are described for measuring attenuation@ one being that for modelling spectral attenuation: ?C method A: cut-back; ?C method B: insertion loss; ?C method C: backscattering; ?C method D: modelling spectral attenuation. Methods A to C apply to the measurement of attenuation for all categories of the following fibres: ?C class A multimode fibres; ?C class B single-mode fibres. Method C@ backscattering@ also covers the location@ losses and characterization of point discontinuities. Method D is applicable only to class B fibres. Information common to all four methods appears in Clauses 1 to 11@ and information pertaining to each individual method appears in Annexes A@ B@ C@ and D@ respectively.