Stock index futures contracts use margin trading. Generally, a contract can be bought and sold only by paying about 10- 15% of the contract face value. On the one hand, it improves the profit space, but on the other hand, it also brings risks, which requires daily settlement of profits and losses. After buying a stock, the book profit and loss are not settled before selling. However, stock index futures are different. After the transaction, the contract held in hand should be settled at the settlement price every day, and the book profit can be withdrawn, but the book loss (that is, additional margin) must be made up before the opening of the next day. So the stock index 1509 will be settled at 15: 15 every afternoon. If you don't settle accounts by yourself, the system will force leveling!