This part of IEC 60793 establishes uniform requirements for the monitoring of changes in optical transmittance, thereby assisting in the inspection of fibres and cables for commercial purposes. This standard gives two methods for monitoring the changes in optical transmittance of optical fibres and cables that occur during mechanical or environmental testing, or both. It provides a monitor in the change of optical transmission characteristics arising from optical discontinuity, physical defects and modifications of the attenuation slope: - method A: change in transmittance by transmitted power; - method B: change in transmittance by backscattering. Methods