《汉书·志·食货志上》
因此善于按平价购粮储存的人，一定小心观察每年有上、中、下三种成熟程度，上熟能收到原来的四倍，最后剩四百石；中熟收获是原来的三倍，最后还剩三百石；下熟是原来的一倍，最后还剩一百石。
是故善平籴者，必谨观岁有上、中、下孰。上孰其收自四，余四百石；中孰自三，余三百石；下孰自倍，余百石。
Therefore, those who are good at buying and storing grain at a fair price must carefully observe that there are three degrees of maturity each year: the upper maturity can receive four times the original amount, and finally four hundred stones are left; the middle maturity is three times the original harvest, and finally three hundred stones are left; the lower maturity is the original amount, and finally one hundred stones are left.