LME is not a futures contract, but a spot contract. Every day there are contracts with different terms (such as 3M, 6M, etc.). ) is generated. Strictly speaking, you must wait until the delivery date. For example, you bought aluminum for three months on June 25, and you will take money to deliver aluminum after three months. However, a month later, on July 25th, aluminum has gone up, and you want to sell the aluminum you bought. At this time, you can short, which is a new spot transaction. For example, it is also three months, and you must deliver the aluminum on June 25th. In order to provide you with the convenience of trading, you are allowed to adjust the schedule in the system, which is equivalent to getting the aluminum you can get on September 25 in advance and selling it on July 25. Therefore, there is an exchange fee for the price increase and discount in the middle.