The monetary system of the Western World is based on the agreement on the establishment of the International monetary Fund （IMF）, which was made at Bretton Woods, New Hampshire （USA）, in 1944. The two principal purposes of the IMF are to promote exchange stability and to help member countries overcome temporary difficulties in their balance of payments. Under the IMF system, the US dollar is the key or leading currency. Each member country of the IMF undertakes to establish a parity of its currency in terms of gold and the US dollar and to keep fluctuations of the dollar exchange rate -- or, more exactly, the spot rate within the limits of the band or fluctuation margin. Originally, the band was 2 per cent （1 per cent on either side of the parity）; in December 1971 it was widened to 4.5 per cent （2.25 per cent on either side）, the upper and the lower intervention point. Each member country's central bank must, if necessary, buy or sell dollars to keep the dollar rate from falling below the lower or rising above the upper intervention point. In this manner, the other currencies, among themselves, cannot deviate from one another by more than double the fluctuation margin , or 8 per cent. 西方世界的貨幣體系是根據(jù)1944年在美國新罕布什爾州布雷頓森林制定的關(guān)于建立國際貨幣基金組織協(xié)議而形成的。國際貨幣基金組織的兩個(gè)主要宗旨是促進(jìn)匯率穩(wěn)定和幫助會(huì)員國克服國際收支方面的暫時(shí)困難。在國際貨幣基金組織體系下，美元是關(guān)鍵貨幣。國際貨幣基金組織的每一個(gè)成員國承擔(dān)著穩(wěn)定本國貨幣與黃金和美元平價(jià)的責(zé)任，并使美元匯率——或者，更準(zhǔn)確地說——美元現(xiàn)匯匯率的波動(dòng)限制在規(guī)定的幅度內(nèi)。最初，波動(dòng)幅度為2%（在平價(jià)上下各1%）；1971年12月，這一波幅擴(kuò)大為2.25%，即上下干預(yù)點(diǎn)。每個(gè)成員國的中央銀行在必要時(shí)應(yīng)買進(jìn)或拋售美元，使美元匯率下降的幅度不低于最低點(diǎn)，或者上升的幅度不超過點(diǎn)。以這樣的方式，其他貨幣之間相互偏離的幅度不能超過波動(dòng)幅度的兩倍，或者說，不能超過8%。
The parities can be changed if need be, but changes in excess of 10 per cent require the approval of the Fund. Parity changes have to be made to correct an imbalance resulting from a permanent improvement or deterioration of a country's competitive position. If, for example, a country has a lower rate of inflation than the other countries, its exports will increase and its imports decline. The growing demand for the currency of this country will cause its external value to appreciate, but since under a system of fixed or pegged parities，exchange rate fluctuation are limited----a point will be reached from which the currency will become increasingly undervalued. If, on the other hand, a country has a higher inflation rate than the other countries, the opposite will be true and the currency of this country will become increasingly overvalued.Such an imbalance is further aggravated by a speculative run out of the overvalued currency into the undervalued one. Therefore, it will eventually be necessary to upvalue the undervalued currency and/or to devalue the overvalued one. 如果需要，平價(jià)可以調(diào)整，但調(diào)整幅度超過10%，須經(jīng)基金組織批準(zhǔn)。進(jìn)行平價(jià)調(diào)整的目的是為了糾正由于永久性地改善一國的競(jìng)爭(zhēng)狀況，或一國競(jìng)爭(zhēng)地位惡化而造成的國際收支失衡。比如，如果一國的通貨膨脹率低于其他國家，該國的出口將會(huì)增加，進(jìn)口將會(huì)下降。對(duì)該國貨幣需要的增加將使其貨幣的對(duì)外價(jià)值上漲，但是，因?yàn)樵诠潭▍R率或釘住關(guān)鍵貨幣的制度下，外匯匯率的波動(dòng)是受到限制的 —— 上漲到某一點(diǎn)后，該貨幣就會(huì)不斷貶值。另一方面，如果一個(gè)國家的通貨膨脹率高于其他國家，就會(huì)出現(xiàn)相反的情況，該國的貨幣就會(huì)不斷的升值。這種國際收支不平衡的狀況會(huì)因?yàn)橥稒C(jī)活動(dòng)而進(jìn)一步加深，即由于價(jià)值高估的貨幣大量流入貨幣價(jià)值低估的國家所造成。因此，提高低估貨幣的價(jià)值和/或降低高估貨幣的價(jià)值，最終成為必然?！?BR>