Per its DESCRIPTION, this Counter64 counts fixed-size blocks of the signal found to contain one or more bit errors, the near-end block-error tally that the errored-second counters are derived from. Because this is a lifetime counter that only resets on an explicit clear, a reading here means individual error blocks have piled up on the near-end signal on this OC-n (SONET) port, accumulated over the port's entire service life, not merely since the last reboot. For example, 200 errored blocks spread over years of service is unremarkable, but the same count in a single day would point at active fiber degradation.