BEIJING, Jan. 15 (Xinhua) -- The central parity rate of the Chinese currency renminbi, or the yuan, weakened by 21 basis points to 6.5637 against the U.S. dollar on Friday, according to the China Foreign Exchange Trading System.

　　In China's spot foreign exchange market, the yuan is allowed to rise or fall by 2 percent from the central parity rate each trading day.

　　The central parity rate of the yuan against the U.S. dollar is based on a weighted average of prices offered by market makers before the opening of the interbank market each business day.