This read-only Unsigned64 reports how much the aggregate transmit errors count increased since the previous stats-polling interval recorded in this one archived historical sample of an interface's error-statistics, i.e. the per-interval rate rather than the lifetime total. A nonzero value here means new failures of this specific kind are occurring right now on this link, not just accumulated history, since this is the transmit-side counterpart to the receive-error rollup for this same interface, used as a first-pass check before looking at its deferred-transmission or internal-MAC-transmit detail. For example, a rise here on a port whose receive counters stay clean points the investigation specifically at this interface's transmit path rather than the far-end device, which this delta field would show as a sudden nonzero reading in a single interval.