General situation: opening reference price = closing price of the previous trading day.
Ex-dividend date: reference price at the beginning = ex-dividend reference price.
The value generated by comparing the latest transaction price (or closing price) of the current trading day with the closing price of the previous trading day is generally expressed as a percentage. In the China stock market, there is a limit to the rise and fall, so there is a saying of "limit to the rise and fall". The latest transaction price of the day is positive if it is higher than the closing price of the previous trading day, and negative if it is lower than the closing price of the previous trading day.
Extended data:
The fluctuation range is not only different in different stock markets, but also changes with time in the same market. Generally speaking, the fluctuation range depends on the stock market and the political and economic situation behind it.
Often in the era of great changes, the ups and downs are too big to control, either the excessive false prosperity of the market or the collapse of the stock market. In both cases, the fluctuation range is actually uncontrollable and uncertain, which is far from the optimal level.
Baidu encyclopedia-ups and downs