The central parity rate of the Chinese currency renminbi, or the yuan, weakened 249 basis points to 6.6444 against the US dollar Thursday, 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 % from the central parity rate each trading day. 
The central parity rate of the yuan against the US dollar is based on a weighted average of prices offered by market makers before the opening of the interbank market each business day.