the alternative to a perpetual system is the periodic inventory system, in which purchases are added to the beginning inventory , the ending inventory 's count andcost are subtracted, and the difference is cosidered the cost of materials issued. Even in a perpetual system periodic physical counts are necessary to discover discrepancies between the actual count and the materials records. Discrepancies may be due to errors in transferring invoice date to the records, mistakes in costing requisitions, unrecorded invoices or requisiton, or spoilage, breakage, and theft. In some enterprises, plant operations are suspended periodically for a physical inventory to be taken. in others, internal auditors or inventory crew count one or more stock