What must be established to accurately measure elevation changes?

To accurately measure elevation changes, establishing a control point is crucial. A control point serves as a fixed and recognizable reference location on the ground that has a known elevation. This known elevation allows surveyors and engineers to determine the height of other points by referencing the control point. It provides a stable datum from which all other measurements can be compared, ensuring consistency and accuracy in elevation data.

Control points are particularly important in surveying and construction because they help to mitigate errors that could arise from variable conditions or equipment calibration. By using a control point, any elevation measurements taken subsequently can be traced back to this reliable reference, making the data meaningful and trustworthy.

In contrast, while reference points and baseline measurements might provide some context and assist in various surveying tasks, they do not inherently establish a fixed elevation benchmark. Standard conditions are less relevant to the relationship between elevation measurement and control points, as they pertain more to the environment where the measurement is taken rather than the benchmarks themselves. Thus, the establishment of control points is essential for accurate elevation change measurement.