This reports the lowest total received optical power across the whole multiplexed line during the bin. Because this reading is a cumulative, non-resettable running figure tracked only from a single start reference rather than any fixed bin, 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, accumulated since this row's single start reference, with no periodic reset.