The optimal period span is 1. According to relevant public information. Cycle is a book written by Howard Marx, published by CITIC Publishing Group, 20 19. Every investor wants to know his position in the cycle. In other words, people are eager to know whether to increase investment and stay in the market, or whether to sell decisively and leave the market. Everyone knows that the market cycle fluctuates, however, most investors often only think of the first layer of shallow thinking in the market cycle.