We want to calculate actual product cost from the BOM. (we have the extension installed)

Does this create a double entry?

Inventory materials in the BOM where purchased with a purchase order and put into inventory. Then consumed to make a product.  When the product cost then takes the total of BOM costs doesn't that create a double entry of the same items?
(ie. a screw was purchased, expensed and put in inventory.  Then it is used to make a product. So the final product cost is derived from the BOM - that screw is getting entered as a cost again.)

OR does Odoo automatically recognize this in the back end and not double expense the items used to manufacture products?