What does a level instrument primarily measure?

A level instrument primarily measures the difference in height between points, which is crucial in surveying and construction activities. This instrument is designed to establish a horizontal line of sight, allowing surveyors to determine relative elevations accurately. By setting up the level instrument at a known height and looking through the telescope at various points, the operator can assess how far up or down the points are in relation to that reference level.

Understanding the elevation differences is vital for tasks such as grading, drainage planning, and ensuring that construction components fit together correctly. This capability makes the level instrument essential for maintaining proper alignments in various engineering and architectural projects, as even small discrepancies in height can lead to significant issues in structural integrity or functionality.

The other options do not accurately describe the primary function of a level instrument. It does not measure material weight, angles of elevation, or distances between two points directly; rather, those measurements are typically addressed using other specialized tools in surveying, such as theodolites for angle measurement or tape measures for distance.