Crossword Genius

Old mark used in complex cash agreement with China for currency control (8,4,9)

Ross

I believe the answer is:

exchange rate mechanism

I'm a little stuck... Click here to teach me more about this clue!

'old mark used in complex cash' is the definition.
I know nothing about this answer so I can't judge whether this works.

'agreement with china for currency control' is the wordplay.
I cannot really see how this works, but
an anagram of 'agreement' is 'ngerateme' which is present in the answer.
an anagram of 'china' is 'chani' which is located in the answer.
This may be the basis of the clue (or it may be nonsense).

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I've seen this clue in The Times.
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