This read-only counter reports the measured optical power arriving at this port's receiver, in millidecibels relative to 1mW, shown as dBm in UIs. An admin watches this value to confirm the incoming signal is within the receiver's specified operating range, since too-low power causes bit errors and too-high power can saturate the detector. A reading of -8000 mdBm (-8.0 dBm) is a healthy signal level for most SFP receivers, while a sudden drop toward the -100000 mdBm not-supported marker or a very negative real reading signals a fiber break or dirty connector.