A WEAK currency, despite its appeal to exporters and politicians, is no free lunch. But it can provide a cheap one. In China, for example, a McDonald’s Big Mac costs just 14.5 yuan on average in Beijing and Shenzhen, the equivalent of $2.18 at market exchange rates. In America, in contrast, the same burger averages $3.71.
That makes China’s yuan one of the most undervalued currencies in the Big Mac index,