What is the difference between by-product and co-product and how do you differentiate them in a BOM?

In case of Co-product costs are settled with a apportionment structure. In case of By-product the price of this by-product is credited to the order or the material stock account of the lead material being manufactured. Co-Product as well as by-product are defined as BOM Components/Items. Both of them have negative quantities. ( Not all negative quantity items fall under these categories!). When BOM is created for FERT , you can see one indicator in COMPONENT DETAILS screen for co-product. You need to define the co-products with this special indicator .