The count of available seconds since the beginning of the test. Available seconds equals the total test time minus any unavailable seconds.

The count of Degraded Minutes since the start of the test. A Degraded Minute occurs when there is a 10‑6 bit error rate during 60 available, non‑severely bit errored seconds.

The number of seconds with at least one error.

The count of error free seconds since the beginning of the test. Error free seconds equals the total test time minus the number of errored seconds.

This is the count of Severely Errored Seconds since the beginning of the test. A second with a bit error rate of 10‑3 or higher is a severely errored second. Severely errored seconds are not counted during unavailable time. Loss of signal (LOS), loss of frame (LOF) and loss of pattern synchronization (LOP) are treated as severely errored seconds.

This is the count of UnAvailable Seconds that have occurred since the beginning of the test. Unavailable time begins at the onset of 10 consecutive severely errored seconds, and ends after 10 consecutive non‑severely errored seconds. The onset of unavailable seconds cause the SES count to be adjusted downward by 10. When unavailable time ends, the UAS count is adjusted downward by 10.