Long Order (Buy): After the investor opens a long position, if the investor wants to close the position, that means investors need to sell the products they bought, so after opening a position, they need to use the "Selling Price" which is the real-time closing price. Short order (Sell): After the investor opens a short position, if the investor wants to close the position, that means investors need to buy the same amount of products again, so after opening a position, they need to use the "Buying Price" which is the real-time closing price.