US Mint pricing of numismatic products

From page 42 of the Mint's 2007 Annual Report:
"United States Mint-owned platinum, gold, and silver are valued at the lower of cost or market using a weighted average inventory methodology."
Anyone have a clue as to the calculations used in this methodology?
"United States Mint-owned platinum, gold, and silver are valued at the lower of cost or market using a weighted average inventory methodology."
Anyone have a clue as to the calculations used in this methodology?

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For example, if the Mint bought gold at 930, they have to value it at 880 or whatever the closing London fix is on Sept 30, the end of their fiscal year.
I hope that clarifies things for you