This International Standard describes the launch condition requirements used for measuring multimode attenuation in passive components and in installed cable plants. In this standard, the fibre types that are addressed include category A1a (50 μm /125 μm) and A1b (62,5 μm /125 μm) multimode fibres, as specified in IEC 60793-2-10. The nominal test wavelengths detailed are 850 nm and 1 300 nm. This standard may be suitable for multimode attenuation measurements for other multimode categories and/or other wavelengths, but the source condition for other categories and wavelengths are not defined here. The purpose of these requirements is as follows: • to ensure consistency of field measurements when different types of test equipment are used; • to ensure consistency of factory measurements when different types of test equipment are used; • to ensure consistency of field measurements when compared with factory measurements. This standard describes launch condition requirements for optical attenuation using sources with a controlled encircled flux (EF).