This object reports the effective, currently-in-force quality level of a specific T4-table candidate source, computed the same way as its T0 counterpart from received QL, forced or configured QL, and any fault-driven override, and it is this value the T4 selection algorithm actually uses to rank candidates for external output distribution. It matters because it directly explains why one candidate source, rather than another, is currently feeding a given T4 output, even when multiple sources appear physically healthy. If a lower-priority-looking source has a higher effective QL here than the presumed primary, that explains why the T4 selection algorithm picked it instead.