One of the important things in laboratories is the control of inventory. Lot labels are essential to make sure that older inventory is used before newer inventory so that, hypothetically, there is never a supply that expires. Lot labels can be used to communicate that a certain supply is to be used first because it has been in stock the longest, or on the opposite end, certain lot labels can clarify that this particular stock has just come in and should not be used until all earlier stocked supplies are used up. Lot labels are also used in other departments throughout the hospital, but their essential purpose remains the same: keep proper inventory of the stock available for use. While lot labels communicate what supplies should be used due to expiration dates, equipment check labels and custom calibration labels clearly state which supplies should be used because they have been tested and checked for proper function.