When entering sales data in Backbar, the time periods for sales data are determined when you have completed and saved inventory sessions.
All time periods are based on an opening and closing inventory. If you take inventory monthly, you can enter sales data for monthly periods.
Or, weekly if you take and close each week.
Backbar uses the sales data to calculate Cost of Goods Sold in the Cost of Goods Sold report found under Inventory Reports.
For accurate Cost of Goods Sold data, you need to keep accurate inventory counts and match the sales data with inventory session time periods.