China faces an urgent task of restoring credibility to its exchange-rate policy after it has sowed confusion in global markets and other central banks in recent months. To that end, China's central-bank chief sought to reassure investors and finance officials in Shangai this week that Beijing has a game plan in place to prevent a sharp fall in the Chinese yuan. Zhou Xiaochuan ruled out China using competitive devaluation to aide exports, repledged its commitment to a more market-oriented currency policy, and at the same time left China plenty of wiggle room for exchange-rate maneuvering. On whether Mr. Zhou succeeds at anchoring market expectations, the jury is still out.