Pos Application

I am developing a POS (Point of Sale) application that should be able to calculate the average price. Here's the deal, I do not know what it is and how it is calculated for consumer products. I just got this requirement. All I know is this, that there is no way to know from which particular stock of goods, a product was sold from. Has anyone done something similar, please help me on this. or if you could suggest me resources.

I'm not very good with the vocabulary of business so please ask if there are ambiguities in this problem statement.

As a retailer, I'm not sure I understand your problem.

Every product in stock can be identified as part of that stock by its product code. Once the code is put into the program, the program should be able to reduce the inventory level for this specific group.

Example: The stock is stored in two locations. The stock code for the product A can be A-01 or A-02. When the product code is entered, the program knows not only what happened, but the group which he had shares.

Is that answer your question?