A fast-food burger has quietly measured currencies against each other since 1986

The Economist created the Big Mac Index in 1986: comparing a Big Mac's price across countries, converted into a single currency, gives a rough, deliberately tongue-in-cheek gauge of whether a currency is over- or under-valued against purchasing power parity. Decades later, economists still cite it as a memorable shorthand for a genuinely complicated idea.

— Pam Woodall, The Economist, Big Mac Currencies — September 1986