China's stock index futures opened lower Tuesday, with the contract for settlement in September, the most actively traded, down 15.6 points to open at 2,261.6. The contract for settlement in October dropped 18.6 points to open at 2,274, and the December contract retreated 16.4 points to open at 2,299.4. The contract for settlement in March 2013 lost 11.6 points to 2,346. 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.