Huangk 1 199 (in-station contact ta) Generally speaking, different letters represent significant values. Xchaosky (intra-station contact ta) means that the numerical values marked with different letters are significantly different, but statistically speaking, there is no significant difference for the same letter. Strictly speaking, the standard deviation should be added after each value, and then whether there is a significant difference between the two values in the same group (the level of significance can be set by yourself, for example, P < 0.05) is not rigorous enough, and it will be indicated under the general article list unless it is junk Chinese journal articles.