When you purchase and sell products there are various methods in which you can track your costs and the overall value of your inventory. By default, Odoo uses the standard cost of your product that you specify for all calculations. With this method, if you change the cost in the product record you can re-run your reports and see the change reflected.

Many times, however you want the ability to track your product purchases and sales more accurately using a removal strategy. Typically, this is either FIFO (First in First Out) or LIFO (Last in Last Out). In FIFO operations the first product you purchase is the first product you sell. This affects your costing and inventory valuation because you may have purchased products at different prices and you may have also sold products at different prices.