What is a permanent reference point used by surveyors to measure differences in elevation known as?

A benchmark is a permanent reference point established by surveyors to measure differences in elevation. These benchmarks are often marked with a metal disc or a similar marker, indicating a precise elevation above sea level. This allows for accurate measurements and calculations in construction, land surveying, and various engineering projects.

Benchmarks provide a reliable and consistent basis for determining the elevation of other points in the surrounding area. They are critical tools in ensuring that land development and construction are conducted with the correct elevations, which is essential for drainage, grading, and ensuring the integrity of structures.

In contrast, while a point of interest might be a location of significance, it does not serve the specific purpose of measuring elevation. An elevation marker could imply various temporary markers but lacks the permanence associated with a benchmark. Finally, a landmark is typically a recognizable feature in a landscape but does not provide precise elevation measurements.