As regards the length of participation, the Treaty foresees a minimum of two years prior to the examination of convergence. This should certainly not prevent a Member State from remaining within the mechanism for more than two years, if this is deemed supportive in accompanying real and nominal convergence.
With respect to Bulgaria and its monetary integration plans, it is important to note that ERM II can accommodate features of a number of exchange rate regimes, including currency boards, so that countries operating currency boards might not be required to go through a double regime shift.