This is the lowest value recorded during the current performance-monitoring interval of the raw bit error ratio measured on the incoming optical signal before forward error correction (FEC) has had a chance to correct any errors, expressed as a bit-ratio. This is the cleanest moment of the interval, useful for confirming the underlying fiber path is capable of a low error floor when conditions are favorable. For example, on a clean, well-engineered span, an admin would expect bitErrorRatePreFecMin to sit near the noise floor for most intervals, with only environmental swings nudging it slightly higher.