This PerfCounter64 counts Unavailable Seconds encountered by a SONET/SDH Section during the history bin, accumulated once the section has been in a severely errored state for ten consecutive seconds. Section UAS is the metric an admin pulls to quantify true outage duration at the physical layer for reporting against a circuit's availability commitment. If ocnStmHistorySectionUASs totals 300 seconds for a 15-minute history bin, that means the section was declared unavailable for roughly a third of the interval, which is a very different severity than the same number of plain errored seconds.