2011 L2 Notes Book2 Page14 Periodic and Perpetual Inventory system

2011 L2 Notes Book2 Page14 Periodic and Perpetual Inventory system里面一段话：

In the case of FIFO and specific identification, ending inventory values and COGS are the same whether a periodic or perpetual system is used. Conversely, there can be significant diferences in inventory values and COGS when using weighted average cost and LIFO basd on the system used.

这段话如何理解啊？高手能否举个例子说明下呢？多谢大侠