Argentina's Convertibility System differed in several key respects from Hanke's original proposal, however. In October 1991, the year the system was implemented, Hanke warned in a "Wall Street Journal" op-ed that the Convertibility System could begin to function as a central bank, and eventually collapse. This prediction came true in the late 1990s, as the Argentine Convertibility System began to function like a central bank and engage in sterilization. Hanke wrote many articles showing that the Convertibility System was not a currency board.