What is a backsight in surveying?

Answer: B — rod reading taken on a point of known elevation

A backsight in surveying refers specifically to a rod reading taken on a point of known elevation. This measurement is crucial in leveling because it establishes a reference point from which other measurements can be taken. By recording the elevation of a known point, surveyors can then determine the relative heights of other points by taking further readings, allowing them to create a comprehensive elevation model of the terrain. When conducting leveling in surveying, starting with a known elevation enables the calculation of differences in height. This process ensures that all subsequent readings are accurately referenced back to a fixed point, leading to reliable data for construction and design purposes. This foundational method is essential for ensuring the integrity and accuracy of any survey work.