A perpetual inventory system keeps a running record of the amount of inventory on hand. The physical quantity of inventory on hand at any time should match the unit balance in the inventory account. A periodic inventory system does not track the dollar amount of inventory on hand. In this system the ending inventory and cost of goods must be determined by physically counting the goods on hand at the end of the period. In the periodic inventory system, the cost of goods sold may not be accurate because the calculation assumes that goods not available at the time of the physical count have been sold. There is no way to determine whether unavailable goods have been stolen or wasted (Revsine, et al, 2015). But a perpetual system provides more precise records because it instantly tracks inventory changes (Ingram,