The four-hour main futures contract is the main futures contract of the month: futures investors choose the most active monthly transactions. In the fixed market for six months in a row, focus on the long-term of three months.

With the passage of time, whether it is the active month of continuous quotation or the forward month of fixed offer, it will become the near month until the delivery month.

The so-called "changing the month" means that the original contract is settled near the matching month, and a new contract is established in the most active month (in the market of fixed trading, it is a forward month). Under normal circumstances, changing the month is to keep the number of contracts unchanged and the direction of buying and selling unchanged.