nbsCoherentStatsAveSOP is read-only and holds the average state of polarization (SOP) rate of change observed on this coherent optical interface since statistics collection last started or was cleared (nbsCoherentStatsState), i.e. how fast the signal's polarization is rotating/drifting on the fiber, a proxy for physical fiber disturbance (vibration, bending, temperature swings); not-supported is encoded as 0xFFFFFFFF. Unit measurement: 1 rad/s. A sysadmin treats it as a longer-run baseline for this specific optic/fiber path, useful for spotting a slow drift in link quality that a single quarterHour or twentyfourHour sample in nbsCohpmCurrentTable might not reveal.