The Art of War by active 6th century B.C. Sunzi

15. Hence a wise general makes a point of foraging on the enemy. One

cartload of the enemy’s provisions is equivalent to twenty of one’s own, and likewise a single _picul_ of his provender is equivalent to twenty from one’s own store. [Because twenty cartloads will be consumed in the process of transporting one cartload to the front. A _picul_ is a unit of measure equal to 133.3 pounds (65.5 kilograms).]