Economist's Big Mac index

The Economist's "Big Mac Index" (see here) is always interesting (see chart below, click to enlarge).  The Economist describes it as follows:

THE Economist’s Big Mac index is a fun guide to whether currencies are at their “correct” level. It is based on the theory of purchasing-power parity (PPP), the notion that in the long run exchange rates should move towards the rate that would equalise the prices of a basket of goods and services around the world.