This factor measures the price change of a stock in the past 20 trading days by calculating the ratio of the current closing price (close_t) to the closing price 20 trading days ago (close_{t-20}). This ratio represents the 20-day interval return. A value greater than 1 indicates that the stock has been on an upward trend in the past 20 trading days, and a value less than 1 indicates that the stock has been on a downward trend. The core of this factor is to determine whether the market is mainly driven by momentum effect or reversal effect by analyzing this ratio. When it is observed that the factor value is positively correlated with future returns, it indicates that there is a momentum effect in the market; conversely, if the factor value is negatively correlated with future returns, it indicates that there is a reversal effect. It should be noted that the trading day here refers to the day when the stock is actually traded, not the natural day. In practical applications, this factor is usually used in combination with other factors and risk management models.