This Counter64 tallies ATM cells transmitted out through the circuit marked CLP0 (high priority), the egress counterpart to circuitInCLP0Cells, showing how many of this circuit's protected-priority cells actually reached the far end. Comparing this against circuitInCLP0Cells lets an admin confirm that essentially all high-priority cells that entered the circuit made it out, since any meaningful gap here (beyond what circuitInCLP0CellsDiscard already explains) would indicate unexpected cell loss for traffic that's supposed to be protected. For example, an admin would expect circuitInCLP0Cells minus circuitInCLP0CellsDiscard to closely match circuitOutCLP0Cells, and any unexplained shortfall would warrant investigating the ring path itself.