There is no futures index in China, only index futures (note that these are completely two concepts, index futures, such as stock index futures). The term refers to the average weight of various futures, such as PTA futures, PTA150916011605, etc. And the calculation of individual commodity index is relatively simple. However, the comprehensive index (such as chemical index) is more complicated, because the official does not have this index to calculate the average weight of all PTA plastics, methanol and PVC, so each trading software calculates it according to its own reasons, and gives different contracts and different weights to different commodities, so naturally the results are completely different.