This reports the lowest total received optical power across the whole multiplexed line 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 deep line-wide minimum here typically lines up with a protection event or amplifier restart affecting every wavelength on this fiber simultaneously. For example, a total OTS minimum several dB below the bin's average, timed to a logged amplifier reset on this line, confirms the dip was line-wide rather than isolated to one channel, so far within today's still-open 24-hour interval.