The most accurate way to determine the altitude of a point in the geodetic network is a method called direct leveling. It consists of comparing two graduated level rods, one placed at the point to be measured (B), the other at a nearby point, the altitude of which is already known (A). An optical level placed at an equal distance between the two level rods determines the spot grade (difference in altitude) between the two points. This procedure is performed from point to point over the entire territory starting from base level (sea level).