Why is PPP impossible to achieve, atleast comprehensively? Because of every reason: commodities and their manufacture properties, the market-nature of a commodity, international trade and social politics and what not. Economic organizations and Banks and trade orgs and companies can merely learn this gradually and implement them with caution and wit but not devise a comprehensive PPP absolute value even as a functional dependence. They can only do so based on a particular commodity. When all commodity properties are known only their values can have a determinable PPP value.