It follows that the rate between 2 currencies should naturally adjust so that a basket of goods and services costs the same in both currencies.
The index has also given rise to the word burgernomics. The Economist has been publishing it annually since then. Pam Woodall introduced it in September 1986. The Big Mac index is an informal way of measuring Purchasing Power Parity (PPP). Why non-tradable goods should be globally equal.