A supplier invoice shows what you bought. It does not, by itself, show the cost associated with a period’s sales. Bring the opening stock, purchases and closing count together before interpreting your restaurant’s COGS.
Sales, gross profit, operating profit and cash tell different parts of the story. Use a clear definition and a worked example before deciding which number to improve.
Start with a consistent inventory count and a clearly defined sales period. Then use food cost percentage to find the questions worth asking about purchasing, portions and waste.