nbsCoherentStatsMaxCD is read-only and holds the maximum chromatic dispersion (CD) observed on this coherent optical interface since statistics collection last started or was cleared (nbsCoherentStatsState), i.e. how much the fiber link has spread out the optical signal in time due to wavelength-dependent propagation delay; not-supported is encoded as 0x80000000. Unit measurement: 1 ps/nm. 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.