What is the primary use of a plumb-bob in construction?

The primary use of a plumb-bob in construction is to check vertical reference. A plumb-bob is a weight suspended from a string that provides a true vertical line, essentially allowing builders to ensure that walls, columns, and other structural elements are perfectly vertical. This is vital in construction to prevent structural issues that could arise from misalignment. The weight of the plumb-bob allows it to hang directly downwards, which is influenced solely by gravity, making it an accurate tool for establishing a vertical point.

In contrast, the other listed options do not accurately capture the main function of a plumb-bob. Measuring horizontal distances, aligning structures, and calculating angles rely on different tools and techniques tailored to those specific tasks. For example, tools like levels or laser sighting devices would more appropriately check horizontal alignments or angles. Using a plumb-bob specifically addresses the need for vertical accuracy, making it an indispensable tool in the construction process.