This part of 61300 describes methods to measure fast variation of attenuation due to mechanical stresses applied on optical fibres and passive optical components during their lifetime. Transient loss measurement shows the effect of fast mechanical disturbances on fibres. These disturbances can be due to several types of action on the device under test, such as: dropping, vibration, bump or manipulation of the fibres. Therefore this measurement will usually be performed on devices exposed to mechanical tests. This method is not designed to measure very fast transient losses (with duration less than 1 ms) that could affect the performance of transmission systems. It is optimised to detect transient losses caused by the mechanical stresses due to the tests prescribed in the component performance standards, whose duration is generally longer than several tens of milliseconds.