Inventory valuation methods determine cost assignment using specific identification, FIFO, or weighted average formulas consistently. Specific identification assigns actual costs to items segregated for specific projects and is unsuitable for large numbers of interchangeable items. For interchangeable inventories cost must be assigned using either FIFO or the weighted average cost formula, applied consistently to inventories of similar nature and use; different formulas may be justified for different nature or use but not merely by geographic location or tax rules. Practical techniques like standard cost and the retail method may be used when they approximate actual cost.