What is the meaning of 'backsight' in the context of leveling surveys?

In the context of leveling surveys, 'backsight' refers to a sight taken to a known point of elevation, which is crucial for establishing accurate height data in the survey process. By observing a backsight, surveyors are able to confirm the elevation of the instrument relative to a benchmark or a reference point. This is an essential step in leveling as it ensures that the measurements taken afterward are based on a reliable starting point.

The significance of backsights lies in their role in establishing a line of sight that is referenced back to a known elevation, allowing for precise calculations and adjustments as surveying progresses. This process is fundamental for achieving accuracy in determining the topographical features of the area being surveyed.