There are four contracts in Shanghai and Shenzhen 300 stock index futures: the current month contract, the next month contract, the next quarter contract and the next quarter contract. As time goes on, the indicators of these four contracts will change constantly. For example, the contract of the current month refers to the contract of September 1209 of 20 1202, while the contract of the current month before delivery refers to the contract of 1208, and so on. This month's contract refers to 1207, 1206 and 65438 in different time periods respectively.