[计] mean repair time, mean time to repair, MTTR[经] mean time to restore
píng jūn xiū fù shí jiān ㄆㄧㄥˊ ㄐㄩㄣ ㄒㄧㄡ ㄈㄨˋ ㄕˊ ㄐㄧㄢ