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: method A: cut-back; method B: insertion loss; method C: backscattering; method D: modelling spectral attenuation. Methods A to C apply to the measurement of attenuation for all categories of the following fibres: class A multimode fibres; 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.