First mention that a sample in the application refers to the little bottles with substance that are sent to the client for testing and that permit them to decide if they want a larger order

Therefore the samples doesnt not mean any substraction of substance on the barrels (as the bottle has very few substance), but will result in a reservation of the substance according to the large order the client is willing to do. The amount reserved in each barrel is displayed all abroad the application

The application is ready to send to different sample for the same large order, this is the concept behind group fields that we will see later.