How is chart vacancy different from normal seat availability?

Chart vacancy shows seats that are empty after the reservation chart is prepared while normal seat availability shows the status before chart preparation. Normal availability changes continuously as passengers book and cancel. Chart vacancy is the final snapshot of vacant berths after all booking activities have stopped. Normal availability includes seats under various quotas that may not be visible to all passengers. Chart vacancy displays only the berths that are actually unoccupied and ready for immediate allotment. Chart vacancy is particularly valuable for last-minute travellers while normal seat availability is better for advance planning.