This is the number of times the Designated IS has changed on this circuit at this level; if the circuit is point to point, this count is zero. Since only broadcast circuits have a DIS election, this counter is meaningfully nonzero only on LAN circuits, and a rapidly climbing count there indicates DIS election instability on that shared segment, often caused by a flapping high-priority router repeatedly winning and dropping the role. For example, a LAN segment showing dozens of DIS changes in an hour points the admin toward a specific unstable, high-priority router on that segment rather than a network-wide problem.