As for military methods: the first is termed measurement; the second, estimation of forces; the third, calculation of numbers of men; the fourth, weighing relative strength; and the fifth, victory. Terrain gives birth to measurement; measurement produces the estimation of forces. Estimation of forces gives rise to calculating the numbers of men. Calculating the numbers of men gives rise to weighing strength. Weighing strength gives birth to victory.
Sun Tzu, The Art of War, c. 450 BCE