Swap lines used to be used to provide dollars for foreign central banks to use to support their currencies in foreign exchange markets.

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In this case, it makes sense to use a foreign exchange broker or understand the detail yourself by using a comparison site such as FX Compared.

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Japan should then use intervention in the foreign-exchange markets to push the yen sharply down, and to hold it down until prices reach their target level.

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But Dino Kos, a former chief of markets at the Federal Reserve Bank of New York who now works for Portales Partners, a research firm, notes that the yuan does not meet one of the most basic requirements of a reserve currency: other countries cannot use it to intervene in foreign-exchange markets because it is not freely convertible.

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Another was to use foreign currency: the bank could lend, or accept a bill of exchange, in one currency and collect its debt in another, building a hidden rate of interest into the exchange rate.

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They can also use it to put controls around activities such as bank account management and foreign-exchange trades.

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Other countries use dual exchange rates to the same end, making it more expensive to acquire foreign exchange for the purpose of investing abroad.

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And how long will Asian countries continue to spend money building up foreign-exchange reserves that earn next to nothing and carry the risk of currency losses, rather than use the money to invest in their own region, which seems set to grow an awful lot in coming years.

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