This PerfCounter64 counts Severely Errored Framing Seconds encountered by a SONET/SDH Section during the history bin, i.e. seconds where the section framing pattern itself was out of sync. SEF indicates the receiver briefly lost byte/frame alignment rather than just seeing bit errors within an otherwise-locked frame, so an admin treats a nonzero SEF count as more serious than an equivalent CV count. If ocnStmHistorySectionSEFs shows several seconds of severely errored framing right after a card reseat, the admin would suspect the framer needed time to reacquire sync rather than an ongoing optical problem.