What is the primary method used in differential leveling?

The primary method used in differential leveling is the consecutive application of direct leveling. This technique involves establishing a benchmark or a starting point, then measuring the height difference between the instrument and a series of points at varying distances. By taking direct readings of elevation from a leveling instrument, surveyors can create a precise elevation profile that accurately reflects the terrain's topography over distances.

In this method, the surveyor uses a leveling instrument, placing it on a stable point to achieve a line of sight across the terrain. Measurements are recorded from backsights and foresights, which are the readings to known points and the next points of interest, respectively. This direct approach ensures that any discrepancies in elevation can be tracked accurately, facilitating an incremental understanding of the land's elevation changes.

Other methods, such as indirect leveling, use calculations or trigonometric principles to derive elevation differences without direct measurement, making them less straightforward compared to the consistency and reliability of consecutive direct leveling. Similarly, while backsights are essential tools in leveling, they serve as part of the direct leveling process rather than as the primary method itself. Lastly, the measurement of horizontal angles pertains more to horizontal control in surveying and is not fundamentally involved in determining vertical elevations through differential leveling.