Coup D'oeil
Among [a general's] skills, the one by which the eighteenth century [C.E.] set the greatest store was that of coup d'oeil, a facility which enabled a commander to grasp the esssentials of a situation and make a speedy and appropriate decision.... (Pirscher)
The process of acquiring coup d'oeil began in peacetime, while the officer was out walking, riding, or hunting. One of the fundamental exercises was to fix a particular measurement in your mind, and the apply it over successively greater distances. The ordinary human pace was assumed to be about 2 feet, and the Prince de Ligne discovered that 80 such paces approximated to the maximum range at which he would consider shooting a hare. Three 80-pace units in turn yielded the length of an Austrian battalion, which came to 240 paces, including the 6 paces allowed for the battalion artillery. The estimation of numbers also demanded practice:
When you see laborers or a herd of cattle in a field, you should guess their number from a distance, then approach more closely and count them, so as to find your margin of error. By repeating this exercise over and over again you acquire a certain assurance of judgment, which will enable you afterwards to make an accurate assessment of a force of infantry or cavalry. (Bessel)
Eventually it became possible to envisage the most peaceful landscape in military terms, and problems and their solutions crowded in upon the mind.
— Christopher Duffy, The Military Experience in the Age of Reason, pp. 140-41
