This counts Errored Seconds at the ODU (Optical Data Unit -- the inner G.709 container that carries the actual client payload): the number of one-second intervals in the bin during which an error was detected on the client payload container carried inside this OTN wrapper. ES at the ODU layer tells an admin how many seconds of the bin saw trouble specifically in the mapped client signal (e.g. the 10GbE or SONET payload riding inside this ODU), which is what actually matters to the service running over this circuit even if the underlying OTU section looks clean; because this bin is the still-open, currently-accumulating interval, its value is only a partial count until the bin's Duration elapses and it rolls into history -- polling it twice a few minutes apart is the fastest way to catch a fault building up in near real time. A typical reading for this bin might be 24 errored seconds, which an admin would compare against the bin's total duration to get a rough availability percentage for this specific interval.