In managing the flow of goods, different groups of items are defined to keep track of small variations of the same product, such as the supplier, expiration date, and purchase price. These groups are called batches, and each batch is given a unique number for identification, called a batch number. This number is assigned by the manufacturer and stays with the batch throughout the entire supply chain and cannot be changed. Compared to batches, the batch number is more official and globally valid, and has a longer lifespan. Items such as food, medical supplies, and health care products must have batch numbers and be displayed on the packaging.