++++ 1 . Common commercial policy - Defence against dumping - Anti-dumping duty - Variable duty equal to the difference between a predetermined threshold price and the price to the first purchaser in the Community - Calculation - Conversion into the currency of the Member State of importation of the threshold price expressed in a foreign currency - Necessity for the value of the two elements used to determine the duty to be converted using the exchange rate applicable on a single date - The rate of exchange applicable at the material date for the valuation of the goods for customs purposes is required to be used in order to determine the price to the first purchaser in the Community as a result of a reference made to the customs legislation ( Council Regulations Nos 1224/80, Art . 1(1 ) and Art . 9, and 551/83, Arts 1 and 2 ) 2 . Common commercial policy - Defence against dumping - Fixing of anti-dumping duties - Discretionary power of the Community institutions - Imposition of a variable duty which is fixed by reference to a threshold price, being the normal value of the goods in the State of exportation, and varies depending on the price paid by the importer - Legality ( Council Regulations Nos 3017/79, Art . 13, and 551/83, Art . 2 ) 3 . Common commercial policy - Defence against dumping - Anti-dumping duty - Variable duty - Method of calculation involving a threshold price - Threshold price fixed in a foreign currency rather than in ecus - Legality ( Council Regulations Nos 2779/78, 3017/79, 3308/80 and 551/83, Art . 2 ) 4 . Common commercial policy - Defence against dumping - Regulation imposing an anti-dumping duty - Subsequent currency movements rendering the duty unjustified - Validity of the regulation not affected - Existence of procedures allowing economic operators to have new economic data taken into account