delivered the opinion of the Court.
The question in this case is the proper rate at which the currency of the invoice of imported goods should be converted into United States dollars under § 522 (c) of the Tariff Act of 1930. 46 Stat. 739, 31 U. S. C. § 372 (c).
On May 13, 1940, petitioner imported into the United States at the port of New York certain woolen fabrics which had been exported from England on May 3, 1940. Payment for the merchandise was made with pounds sterling purchased through the Guaranty Trust Co. of New York in the New York market for cable transfer. The Collector of Customs converted the pounds sterling of the invoice into dollars at the “official” rate of exchange of $4.035. Petitioner claimed that the currency of his invoice should have been converted at the “free” rate of exchange of $3.475138. He paid the higher rate and filed his protest against the Collector’s action under § 514 *85of the Tariff Act of 1930. The Customs Court sustained the protest. 79 Treas. Dec., No. 7, 14. The Court of Customs and Patent Appeals reversed. 143 F. 2d 132. The case is here on a petition for a writ of certiorari which we granted because of the importance of the questions presented.
The “free” rate and the “official” rate have the following origin.
Sec. 522 (a) of the Tariff Act provides that the value of foreign coin as expressed in the money of account of the United States shall be that of the pure metal of such coin of standard value, and that it shall be estimated quarterly by the Director of the Mint and proclaimed by the Secretary of the Treasury. The value of the pound sterling at all times relevant here was proclaimed to be $8.2397. Sec. 522 (b) provides that, for the purpose of assessment and collection of duties upon merchandise imported into the United States, foreign currency shall be converted, wherever necessary, into currency of the United States at the values proclaimed by the Secretary under § 522 (a) for the quarter in which the merchandise was exported. Sec. 522 (b) provides, however, for an exception. That exception is contained in § 522 (c) which reads as follows:
“If no such value has been proclaimed, or if the value so proclaimed varies by 5 per centum or more from a value measured by the buying rate in the New York market at noon on the day of exportation, conversion shall be made at a value measured by such buying rate. If the date of exportation falls upon a Sunday or holiday, then the buying rate at noon on the last preceding business day shall be used. For the purposes of this subdivision such buying rate shall be the buying rate for cable transfers payable in the foreign currency so to be converted; and shall be determined by the Federal Reserve Bank of New York and certified daily to the Secretary of the Treasury, who *86shall make it public at such times and to such extent as he deems necessary. In ascertaining such buying rate such federal reserve bank may in its discretion (1) take into consideration the last ascertainable transactions and quotations, whether direct or through exchange of other currencies, and (2) if there is no market buying rate for such cable transfers, calculate such rate from actual transactions and quotations in demand or time bills of exchange.”
At all times prior to March 25,1940, the Federal Reserve Bank of New York pursuant to its authority under § 522 (c) certified daily to the Secretary of the Treasury one buying rate for the pound sterling. When the present war between Great Britain and Germany was declared, the British Government inaugurated a detailed system for controlling foreign exchange. It required among other things that all persons resident in the United Kingdom sell to the British Treasury at prices fixed by it all foreign currency which they were entitled to sell, and prohibited, with certain exceptions, exportation of foreign currency from the United Kingdom and the purchase and sale of foreign currency in the United Kingdom from or to any person other than an authorized dealer and at prices fixed by the British Treasury. On March 7, 1940, an Order in Council, effective March 25, 1940, was issued by the British Government which provided that certain classes of merchandise1 (whiskey, furs, tin, rubber and jute) might not be exported from the United Kingdom to the United States and certain other countries except when payment had been or would be made to persons resident in the United Kingdom in specified currencies. These currencies included United States dollars or English pounds pur*87chased in the United Kingdom after September 3, 1939, from an authorized dealer in foreign currency. Authorized dealers sold English pounds only at the rate of $4,035, prescribed by the British Treasury, from January 8, 1940, to September 30, 1942, when the present case was tried.
On March 19, 1940, the Federal Reserve Bank of New York notified the Secretary that because of the order of the British Government of March 7,1940, it would certify, beginning March 25, 1940, two rates for the pound sterling — one to be designated as the “free” rate, the other as the “official” rate. The latter was the rate fixed by the British Treasury. On April 15, 1940, the Secretary of the Treasury notified the collectors of customs that until further notice he would publish only the “official” rate; and he directed them to use that rate for assessing and collecting duties on imported merchandise whenever it varied by more than 5 per cent from the value of the pound proclaimed by the Secretary under § 522 (a) of the Act.2 T. D. 50134, 75 Treas. Dec. 370, 371, 5 Fed. Reg. 1447.
On the date petitioner exported his merchandise from England, the Federal Reserve Bank of New York certified to the Secretary of the Treasury that at noon on that day the “free” rate for the English pound was $3.475138 and the “official” rate was $4,035. The Secretary, in accordance with his notification' of April 15, 1940, to the collectors of customs published only the “official” rate. T. D. 50146, 75 Treas. Dec. 388. Since the “official” rate varied by more than 5 per cent from the proclaimed value of the pound for that quarter, the collector used the “official” rate in converting pounds into dollars for the purpose of assessing and collecting duties upon the value of the *88woolen fabrics. The pounds sterling which petitioner used in the purchase of the woolens were not obtained from an authorized dealer as defined in the British order of March 7, 1940, but, as we have noted, through the Guaranty Trust Co. of New York in the New York market for cable transfer. Petitioner claims that the invoice currency should have been converted at the “free” rate of $3.475138 as determined and certified by the Federal Reserve Bank of New York for the date of this exportation.
It was noted in United, States v. Whitridge, 197 U. S. 135, 142, that the assessment of an ad valorem tax on imports involved an ascertainment of the true value of the article taxed as of the date of the tax and that the invoice price was an approximate measurement of that value. As pointed out in that case, the history of the statutes shows a closer approximation to that value as the legislation has evolved. And the enactments made subsequent to the decision in the Whitridge case are consistent with that trend. In the beginning Congress prescribed specific dollar values of specified coins. Act of July 31, 1789, § 18, 1 Stat. 29, 41. Not long after, the President was given authority to prescribe regulations for computing duties on imports where the original cost was exhibited in a depreciated currency of a foreign government. Act of March 2, 1799, § 61, 1 Stat. 627, 673. In 1873 Congress provided for an annual estimate by the Director of the Mint of the full metal value of standard coins of the various nations and a proclamation of the value by the Secretary of the Treasury. Act of March 3, 1873, 17 Stat. 602. That estimate was required to be made quarterly rather than annually by the Act of October 1,1890, § 52, 26 Stat. 567, 624. Then came the Act of August 27, 1894, § 25, 28 Stat. 509, 552, which retained the provision for the estimate and proclamation of metallic values and gave the Secretary of the Treasury power to order a reliquidation at a different value on a showing that the value of the *89invoice currency in United States currency was 10 per cent more or less than the proclaimed value. United States v. Whitridge, supra. The procedure under the latter provision depended on a consular certificate to establish the percentage of depreciation of the currency. T. D. No. 23725, 5 Treas. Dec. 396. There was thus no single source (and none at all in the United States) to which customs officials could look to determine the extent to which foreign currency had depreciated. Moreover, violent fluctuations in foreign exchange rates had occurred after the first World War. It was for those reasons that § 403 (c) was added to the Emergency Tariff Act of 1921, 42 Stat. 9, 17. See S. Rep. No. 16, 67th Cong., 1st Sess., p. 16; H. Rep. No. 79, 67th Cong., 1st Sess., p. 12; Fry & Friedsam v. United States, 12 Cust. App. 486, 489. And § 403 (c) of the 1921 Act now appears as § 522 (c) of the 1930 Act on whose meaning the present decision turns.
This history makes clear the search which has been made for a measure of the true dollar values of imported merchandise for customs purposes which was accurate (see Cramer v. Arthur, 102 U. S. 612, 617) and at the same time administratively feasible and efficient. The formula finally selected is dependent on the actual value of the foreign currency in our own money. The rate for the foreign exchange with which the imported goods are purchased is recognized as the measure of value of the foreign currency; the use of that rate reflects values in United States currency which are deemed sufficiently accurate to serve as the measure of the valuation of the goods for purposes of the ad valorem tax. As noted in United States v. Whitridge, supra, p. 144, the actual “unit of cost” conforms with the truth and the meaning of the invoice.
We would depart from that scheme if we read § 522 (c) as saying that on a given date only one buying rate for a specified foreign currency could be certified by the Fed*90eral Reserve Bank of New York or proclaimed by the Secretary of the Treasury. Dual or multiple exchange rates have resulted in recent years from measures for the control and restriction of foreign exchange and export transactions.3 In the present case the British Government fixed the “official” rate for the purchase of specified commodities for export. One who purchased woolens for export need not acquire pounds at that rate. A lower rate was available and was indeed taken advantage of by petitioner when he purchased pounds to pay for the woolens. If the higher “official” rate is used in the valuation of the woolens, the cost of the goods will be distorted and an inflated value for customs purposes will be placed upon them. Such a result would be quite out of harmony with the history of these statutes and should be avoided unless the result is plainly required by the language of § 522 (c). We do not think it is.
We may assume that the dual or multiple exchange rates which have emerged were not in contemplation when the 1930 Act was passed. As we have noted, they are parts of rather recent measures for the control and restriction of foreign exchange and export transactions. But if Congress has made a choice of language which fairly brings a given situation within a statute, it is unimportant that the particular application may not have been contemplated by the legislators. Puerto Rico v. Shell Co., 302 U. S. 253, 257; Browder v. United States, 312 U. S. 335, 339, and cases cited. Sec. 522 (c) contains no language indicating that the Secretary of the Treasury has any function to perform except the publication of any buying *91rat© which is certified. The determination of the rate is left exclusively to the Federal Reserve Bank of New York. It alone is given discretion in computing it. The duty of the Secretary to publish the certified rate is as clear as the duty of the Federal Reserve Bank of New York to determine and certify it. It is true that § 522 (c) speaks only of the “buying rate.” And that use of the singular rather than the plural is stressed by respondent. We may note, however, in passing that § 1 of the Revised Statutes, 1 U. S. C. § 1, provides that “words importing the singular number may extend and be applied to several persons or things.” Beyond that is the fact that we are construing a provision of a tariff act designed, as we have said, to value imports for customs purposes by means of the buying rate of the invoicé currency. The use of the singular is not inappropriate since there is a buying rate for the foreign exchange used to purchase each separate import. We assume that the “official” rate was the all-inclusive rate and could have been used in payment of exported goods of all kinds. But § 522 (c) means to us that that buying rate is to be used which is in fact applicable to the particular transaction. To look to other transactions for the buying rate is to make a valuation of a wholly hypothetical import, not a valuation of the actual one before the collector of customs. Congress could, of course, choose any standard of valuation, for the purposes of the assessment and collection of duties. But Congress in this situation endeavored to provide a flexible and realistic, not an arbitrary, standard. We can indeed see no difference in principle between the use of one of several rates for the currency of a single country and the use of one of several rates each of which is for the currency of a different country. In each different rates are used to ascertain the value of specific imports. The language of § 522 (c) read against the background of these statutes indicates to us that Congress undertook to provide in each case the rate which *92gives the closest approximation to the value in dollars of the imported merchandise. That purpose would be thwarted if in the circumstances of this case only one buying rate could be used in making the valuation of the goods. The application of the “official” rate to this particular transaction would assume that petitioner imported whiskey, furs, tin, rubber, or jute rather than woolens. The valuation of the woolens would be inflated and a higher duty would be paid than a fair reading of § 522 (c) necessitates.
It is said that this result runs counter to the provisions of § 402 of the Act which require that the value of imported merchandise shall be the “foreign value or the export value, whichever is higher.” But it is not apparent how that policy need in any way be defeated or impaired by the use of the “free” rate of exchange where it is in fact applicable.
Reliance for the other conclusion is also placed on the general authority given the Secretary over the collection of duties on imports 4 and over collectors of customs.5 It is also pointed out that § 624 of the Tariff Act of 1930 provides that “In addition to the specific powers conferred by this Act, the Secretary of the Treasury is authorized to make such rules and regulations as may be necessary to carry out the provisions of this Act.” 6 But these *93provisions merely implement authority which is granted the Secretary and make clear the existence of authority which otherwise might be only implied. They may not be used to detract from the express authority given the Federal Reserve Bank of New York under § 522 (c). But this result is criticized on the ground that it interferes with the control of foreign exchange, which fiscal function has been entrusted to the Secretary, not to the Federal Reserve Bank of New York. It hardly need be pointed out in reply, however, that our decision, like § 522 (c), is concerned only with the assessment and collection of duties upon imports through the use of a formula which Congress designed. If the use of that formula under the changed conditions of these war years is disadvantageous or undesirable, Congress, of course, can change it. But we cannot assume that Congress did not mean what it said when it selected the Federal Reserve Bank of New York rather than the Secretary to perform a restricted function on this single phase of the complicated foreign exchange problem.
Nor is there substance in the argument that the Secretary’s action in publishing only one of the rates certified by the Bank is non-reviewable. Sec. 522 (c) plainly gives discretion to the Bank to determine the buying rate. And for the reasons stated we cannot say that only one buying rate must be determined and certified.7 The exercise of *94the Bank’s discretionary power under § 522 (c) is in the category of administrative or executive action which this Court held non-reviewable in Cramer v. Arthur, supra, and in Hadden v. Merritt, 115 U. S. 25, 27-28. And see United States v. Bush & Co., 310 U. S. 371, 380. But the function of the Secretary in this regard is purely ministerial and is to be contrasted to other situations in which the Secretary is exercising discretionary authority. Cf. Boske v. Comingore, 177 U. S. 459. The power to publish the certified rate may not be exercised in such a way as to defeat the method of assessment which Congress has provided. Cf. Campbell v. United States, 107 U. S. 407. Congress has granted judicial review of the decisions of the collector including the legality of the orders and findings entering into the protested decision. §§ 514-517. If the decision of the collector contravenes the statutory scheme and disregards rights which Congress has bestowed, the fact that he acts pursuant to the directions of the Secretary does not save his decision from review. Campbell v. United States, supra. We think that the use of the “official” rate of exchange in assessing and collecting duties upon these imports transcended the authority of the collector and of the Secretary and that the “free” rate of exchange certified by the Federal Reserve Bank of New York should have been used.
It is finally said that if more than one buying rate may be made applicable to imports from one country,8 confu*95sion and complexity in administration of the Tariff Act will result. But that showing would have to be far more clear and the meaning of the Act much more dubious for us to give those administrative considerations weight in the interpretative process.
Reversed.
Mr. Justice Jackson took no part in the consideration or decision of this case.Subsequent to the exportation of the merchandise involved in the present case this Order was amended, effective June 10, 1940, to include goods of any class or description.
As we have noted, the value of the pound sterling at all times pertinent to this case was proclaimed to be $8.2397.
See United States Tariff Commission, Regulation of Tariffs in Foreign Countries by Administrative Action (1934); Twenty-second Annual Report of the United States Tariff Commission (1938)-p. 1; Southard, Foreign Exchange Practice and Policy (1940) pp. 185 etseq.
“The Secretary of tbe Treasury shall direct the superintendence of the collection of the duties on imports as he shall judge best.” Rev. Stat. § 249,19 U. S. C. § 3. And see Rev. Stat. § 248, 5 U. S. C. § 242.
“The Secretary of the Treasury shall prescribe forms of entries, oaths, bonds, and other papers, and rules and regulations not inconsistent with law, to be used in carrying out the provisions of law relating to raising revenue from imports, or to duties on imports, or to warehousing, and shall give such directions to collectors and prescribe such rules and forms to be observed by them as may be necessary for the proper execution of the law.” Rev. Stat. § 251, 19 U. S. C., Supp. III, § 66. And see Rev. Stat. § 161, 5 U. S. C. § 22.
Sec. 502 (c) of the Act provides that “It shall be the duty of all officers of the customs to execute and carry into effect all instructions *93of the Secretary of the Treasury relative to the execution of the revenue laws; and in case any difficulty arises as to the true construction or meaning of any part of the revenue laws, the decision of the Secretary shall be binding upon all officers of the customs.”
The case is therefore different from Collector v. Richards, 23 Wall. 246. In that case the Director of the Mint certified two values of the franc — one under the provisions of the Act of March 3, 1873, 17 Stat. 602, the other under the Act of May 22, 1846, 9 Stat. 14. The Director of the Mint was uncertain whether the latter act had been repealed by the former. The Secretary proclaimed the rate estimated by the Director under the 1873 Act. This Court sustained a collection *94of duties on that basis, holding that the provisions of the 1873 Act controlled. Thus the decision was that only one value of the franc controlled, not that the power of the Secretary to proclaim the value included the power to choose between two available ones.
It should be noted that where two or more currencies of different character circulate in a foreign country the Treasury has provided for the use of the foreign exchange rate for each, the rate used being the rate for the currency in which the same or similar merchandise is usually bought and sold in the ordinary course of trade. See Customs Regulations of 1937, Art. 776 (a) and (e), as amended by Treas. Dec. 50251 (i) and (j), October 10, 1940.