31 U.S.C. § 5151: Conversion of currency of foreign countries

“buying rate” means the buying rate in the market in New York, New York, for cable transfers payable in the currency of a foreign country to be converted. when merchandise is exported on a day that banks are generally closed in New York, the buying rate at noon on the last prior business day is deemed to be the buying rate at noon on the day the merchandise is exported. The value of coins of a foreign country expressed in United States money is the value of the pure metal of the standard coin of the foreign country. The Secretary of the Treasury shall estimate the values of standard coins of the country quarterly and publish the values on the first day of January, April, July, and October of each year. Except as provided in this section, conversion of currency of a foreign country into United States currency for assessment and collection of duties on merchandise imported into the United States shall be made at values published by the Secretary under subsection (b) of this section for the quarter in which the merchandise is exported. equal to the buying rate at noon on the day the merchandise is exported; or prescribed by regulation of the Secretary for the currency that is equal to the first buying rate certified for that currency by the Federal Reserve Bank of New York under subsection (e) of this section in the quarter in which the merchandise is exported, but only if the buying rate at noon on the day the merchandise is exported varies less than 5 percent from the buying rate first certified. consider the last ascertainable transactions and quotations (direct or through exchange of other currencies); and actual transactions and quotations in demand or time bills of exchange; or the last ascertainable transactions and quotations outside the United States in or for exchange payable in United States currency or foreign currency.