Illustrated Commentary on Nine Chapters, Vol. 1

According to this method, multiplying the width and length in li yields the area in square li. Squaring this gives the number of mu. Since one square li contains 3 qing and 75 mu, multiplying by this value immediately yields the number of mu.

The calculation says: Place the width of 1 li in position. Expand this to 300 bu Chinese unit of length, a pace. Also expand the length of 1 li to 300 bu. Multiply them to get 90,000 square bu as the dividend. Use 240 bu the standard area constant for one mu as the divisor to divide it; this yields 375 mu. Converting this gives 3 qing and 75 mu, which matches the answer.

The calculation says: Place the width of 2 li in position. Multiply by the length of 3 li to get 6 square li. Then multiply by 375 to get 2,250 mu. Converting this gives 22 qing and 50 mu, which matches the answer.

Square Fields

The commentary says: In ancient times, 300 bu made one li. Multiplying 300 bu by itself yields 90,000.