From actually reading the article: Burgernomics was never intended as a precise gauge of currency misalignment, merely a tool to make exchange-rate theory

From actually reading the article: Burgernomics was never intended as a precise gauge of currency misalignment, merely a tool to make exchange-rate theory more digestible. Yet the Big Mac index has become a global standard, included in several economic textbooks and the subject of dozens of academic studies. For those who take their fast food more seriously, we also calculate a gourmet version of the index.