Ancient and modern rangefinders

OAKOC is an Army acronym used for planning operations: it stands for Observation and fields of fire, Avenues of approach, Key and decisive terrain, Obstacles, and Cover and concealment. The first point is therefore the Observation and fields of fire. It means that it is necessary to answer the following questions [1]: What can you see throughout your area? What fields of fire will you have in terms of maximum effective range? How will the weather affect your and enemy’s visibility? First of all, it is required a surveying to measure the ranges of location and fire. Here the noun "range" has the two following senses. It means the extent or limits between which an operation or action is possible. It has also the sense, pertaining to ballistics, which means the distance to which a projectile is or may be sent by a weapon or the distance of the target from the weapon [2]. For what concerns the etymology, “range” as “row or line of persons,” hunters or soldiers, is coming from the Old French “rangier, to place in a row, arrange.” Meaning also “scope, extent” was first recorded 1660s. The sense of “distance a gun can send a bullet” is recorded from 1590s. Therefore, the “ranger” is the agent noun from range (verb), in the modern military sense of “member of an elite combat unit” [3]. An instrument is a “rangefinder,” if it is suitable for determining the distance from the observer. It is therefore necessary for OAKOC. In fact, the noun rangefinder, is used for sighting a gun and also for adjusting the focus of a camera. According to the Websters dictionary [4], it is a measuring instrument (acoustic or optical or electronic) for finding the distance of an object. In gunnery, an instrument, or apparatus, variously constructed, for ascertaining the distance of an inaccessible object, used to determine what elevation must be given to a gun in order to hit the object. Here we will discuss rangefinders, choosing some devices, ranging from the ancient Rome to the modern instrumentation.