This read-only counter reports the number of Severely Errored Seconds recorded on the interface during one completed 15-minute (or daily) PM interval. Because SES flags seconds where the error rate crossed a much higher threshold than a plain Errored Second, admins weight it more heavily when judging whether a link is failing rather than merely noisy. Even a handful of SES counts in a 15-minute window on a transport link usually warrants checking the same interval's slPmIntervalTcaFlag to see if a threshold-crossing alarm also fired.