Field help (CPRPRI) 

The 'cost price' is populated by default with the valuation of the product chosen for the margin calculation (see the valuation methods defined for the Product-Site record) at the time of the creation of the document line and is expressed in sales unit. The various possible choices for the cost price valuation are: Standard price, Revised standard price, Last price, Weighed average price, FIFO price, Lot average price and LIFO price. If the valuation method happened to return a zero value, a default value is used by specifying another valuation method contained in the list previously described. This value is stored in the "document" line.

It is possible to preload this information according to the document transaction used. Still, during the following events, the entered value is systematically replaced by the value originating from the setup of the valuation method for the product, except if this setup determines a null value (in which case the change is saved):

In quote management, the 'lot average price' always returns a null value. A default value is used. During the delivery validation, the 'Lot average price' is used to recalculate the margin and obtain a real margin depending on the shipped lot(s).