nbsCohpmRunningAveSOP is read-only and holds a cumulative statistic since the port was last configured (i.e. since boot-up or the last protocol/FEC/preference change) for the average state of polarization (SOP) rate of change on this coherent optical interface, 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. Because it accumulates from the port's last configuration event rather than resetting every interval, a sysadmin uses it as a long-run baseline for this optic, and a value that drifts far from what nbsCohpmCurrentAveSOP is showing right now can indicate a slow-developing fiber or transceiver issue.