Standby contracts generally refer to basic contracts. Only when the basis is determined when selling can the buyer determine the price at the right time. The final price is the futures price+basis.

For example, in May, the soybean basis contract for September was signed, and the basis was determined to be 200 points. After signing the contract, you can count the prices from May to September. For example, on August 20th, the soybean futures price was 4000, and the selling price was 4000+200 = 4200.