Danish index, also known as TD index, can usually be divided into TD series and TD combination. The basic principle of the two is the same, that is, the market trend is formed by the joint action of buyers and sellers. When the buyer's power is greater than the seller's power, the trend is upward, and vice versa. However, the appearance of the strength of buyers and sellers is dynamic. When the trend rises for a period of time, the buyer's power will inevitably be exhausted, and the market will turn down. The TD index aims to find the region where the trend wants to turn (commonly known as the inflection point). Also based on this theory, there are indicators designed by Yimeng Prophecy Emperor in China. Both indicators successfully predicted the arrival of the bottom of the A-share market in March this year, which can be said to be in step with 100% coincidence.