Count once a week, type your invoice lines and two sales numbers, and the workbook gives you opening plus purchases less closing, against your own target. Each week it shows which items moved, and whether a price change explains it. If nothing moved in price, it happened in the building.

One workbook holds one quarter: thirteen weeks, up to three locations, 300 items and 3,000 invoice lines. You carry the closing count and last prices into a new copy in a few minutes; the guide has the steps. It needs Excel 2019 or later, or Google Sheets, and it ships no benchmark.