This reports the same received optical power for this wavelength, but normalized -- note the syntax is a plain Integer32 rather than the milli-scaled PmInteger32Milli used for the absolute-power fields, i.e. it is expressed relative to an expected/reference level rather than as a raw dBm reading. Because this reading sits in the rolling window of completed 15-minute history bins for this wavelength/line, this normalized form lets a technician compare this value directly across ports or wavelengths of different nominal launch power without doing unit conversion first. For example, a value near 0 means this channel is receiving power essentially where expected; a value around -800 (roughly -8 dB below expected) on this specific OCh flags an anomaly on that one wavelength, within that completed 15-minute window.