The principles for determining the currency area are basically: economic and trade powers; The economy is stable and the exchange rate has not changed dramatically; A country with a freely convertible currency [or a group of countries with an independent currency area and a single currency].
At the same time, we should also consider that its trade volume with China is relatively large.
Generally speaking, it can be said that it is the following countries [or a group of countries with independent currency areas and single currency]:
USA, EU, Japan, UK, Russia, Korea, Singapore, Canada and Switzerland. ...
Of course, it is also possible that this list can be lengthened, shortened and modified.
For simplicity, it is assumed that there is no chance of "arbitrage" in the exchange rates of any three currency areas.
* Note: The use of exchange rate arbitrage in three currency areas means, for example, that the currencies in three currency areas are called A yuan, B yuan and C yuan respectively. The exchange rate at a certain time on a certain day is 1A yuan equals 2B yuan, and 1B yuan equals 2C yuan. However, 1A yuan is not equal to 4C yuan, but 5C yuan. At this time, someone will "arbitrage", that is, for example, use 100 A instead of 500 C, then 250 B, and then 125 A. After three foreign exchange transactions, the profit was 25%. In reality, generally speaking, of course, there will not be such a big profit arbitrage opportunity. Even if there is a much smaller arbitrage opportunity, it will soon be discovered by speculators for arbitrage. Therefore, in an arbitrage opportunity similar to the above, the exchange rate of 5 will first decrease rapidly, and then decrease gradually until it drops to 4.
End of comments.