The Economists's famous Big Mac index - its says the yuan is undervalued. I know for a fact that Ronald McDonald isn't talking his book.

I mean, he wouldn't. If you can't trust Ron, who can you trust?

Assuming that in the long run exchange rates adjust so that $1 buys the same basket of goods everywhere, a cheap burger at market rates suggests a cheap currency too

Most currencies in our chart look cheap against the greenback

For that, thank the Federal Reserve for tightening monetary policy while other central banks loosen, as well as tumbling commodity prices, which have pulled their exporters' currencies down

Check out the yuan!