Refers to the difference between the opening price of the current trading day and the closing price of the previous trading day. In the stock market, the previous period's split is often used as a reference indicator to measure market volatility and changes in investor sentiment. If the previous period's divergence is larger, it means that the market sentiment is more volatile and investors' willingness to trade is stronger; if the last period's divergence is smaller, it means that the market sentiment is relatively stable and investors' willingness to trade is relatively weak. In the futures market, the last period's divergence is relatively weak. Kai is also used to calculate profit and loss, especially when doing high-frequency trading.