What tool is primarily used to determine transit elevation?

A benchmark is a reference point with a known elevation used in surveying and construction to ensure that other measurements can be accurately compared to a known standard. It helps establish a horizontal plane from which other elevations can be calculated. Using a benchmark allows pipe fitters and construction professionals to maintain the required slope and elevation of pipelines, ensuring proper drainage and flow.

When a benchmark is established at a specific elevation, all subsequent measurements can be referenced against it, making it essential for determining transit elevation. This method is reliable and provides consistency across a project.

The other choices, while related to measuring or leveling in construction, do not serve the same primary function as a benchmark. For example, a laser level is a tool used to project a straight line for leveling work, but it requires a reference point like a benchmark to establish elevation. Similarly, the string method calculation can help visualize level lines but can lack the precision and reliability that a benchmark provides. Lastly, a Vernier scale is typically used for measuring distances, angles, or diameters rather than determining elevation directly. Therefore, a benchmark is the foundational tool for accurately determining transit elevations.