i don’t think there is a really good measure of tradables capacity. overall GDP is wrong, since much economic activity is not internationally tradable. exports are an underestimate, the economy produces more tradables than it exports and there may be more tradables capacity than actual production 1/

exports was a “cheap” alternative to GDP that’s readily available, but not “right”. i don’t know what right would be. 2/

by Ricardo do you mean species flow? i don’t think that mechanism really functions in a fiat world, particularly with respect to an issuer of widely accepted fiat. the price level is pretty decoupled from the internat’l balance in modern economies. but that’s maybe not what you’re referring to? /fin