However, marching in absolute lockstep is not necessary, as can be seen in the USA, where certain regions grow faster than others. Growth rates of states and regions within a currency union may differ to some degree. It is the size of the gap between actual and potential growth rates which matters.
If potential output growth rates differ, actual growth rates can differ as well. They do not necessarily indicate a lack of real convergence. VI In the longer run, stability must be built on economic integration. An extensive body of theory has evolved on the characteristics of optimum currency areas. Most important is, that prices and wages must be able to adjust flexibly.