A kitchen that counts stock monthly and prices it at whatever the last invoice said is not measuring food cost — it is producing a number that moves with purchasing timing rather than with consumption.
Vestibel deducts ingredients against a recipe when an order fires, draws them from stock batches in FIFO order at the cost each batch was actually received at, and records every movement in an append-only ledger. The on-hand figure on the item is a cache of that ledger, recomputed inside the same transaction that writes to it.
Count sessions correct drift without destroying history: a line nobody counted stays explicitly uncounted rather than being read as zero, and the correcting movement is computed against live stock rather than the figure on screen when the session opened.