This reports the lowest transmitted optical power for this wavelength during the bin. Because this reading comes from the live 24-hour bin that has been accumulating since the last daily roll-over for this wavelength/line, a transmit-power dip captured here, rather than at the receiver, narrows a fault to the local transponder or its optical path and rules out the far end or the fiber plant. For example, a momentary dip to -3.0 dBm transmit power on this OCh, while receive power elsewhere stays stable, points at a local laser or connector issue on this specific card, so far within today's still-open 24-hour interval.