China's stock index futures opened mixed on Wednesday, with the contract for settlement in May, the most actively traded, down 3.8 points to open at 2,157. The contract for settlement in June opened flat at 2,147.6. The September contract opened 1.2 points higher at 2,130, and the December contract gained 0.6 point to open at 2,144. The stock-index contracts, agreements to buy or sell the Hushen 300 Index at a present value on an agreed date, are designed to allow investors to bet on and profit from either gains or declines in the market. The index futures were launched at the China Financial Futures Exchange (CFFEX) and started trading from April 16, 2010. The CFFEX has set the base value for all the four contracts at 3,399 points.