Xx consecutive three: the contract of the third trading month, counting from the contract of the current delivery month.

Xx consecutive four: the contract is in the fourth trading month of the current delivery month contract.

Therefore, the continuity (contract) of xx is not fixed. For example, today's Shanghai copper continuity is Cu 1508 (the contract delivered in August 2005). After the delivery of Cu1508, the Shanghai copper continuity becomes CU 1509.

As for why the concepts of xx Company III and xx Company IV are introduced, it is because for almost all futures trading varieties, from the current delivery month, the contract trading volume in the third and fourth months is the largest, representing the main trend of market operation, and the continuous price of xx is the closest to the spot price.