The opening price of the next day is 1800, and the cost of holding positions is still 1800, so the position will be closed at the first time, and no profit or loss will be made.
The settlement price is the price used to settle the profit and loss every day, which is the weighted average price of the whole day.
The actual buying and selling prices are the prices at which you open and close positions.
If you do intraday trading, it does not involve the calculation of settlement price.
If you hold a position overnight, calculate your profit and loss distribution according to the settlement price every day.