What is a 'plumb line' used for?

A plumb line is an essential tool used in carpentry and construction for determining vertical alignment. It consists of a string or cord with a weight attached to one end, allowing it to hang freely. When the weight is allowed to dangle, it settles directly downward under the influence of gravity, creating a straight, vertical line.

This vertical reference is crucial for ensuring that structures are built upright and true. For example, when installing door frames, windows, or wall studs, a plumb line helps carpenters verify that these elements are perfectly vertical, preventing structural issues, such as leaning walls or uneven surfaces, that could arise if elements are not properly aligned.

Other options refer to different measurements and tools: measuring horizontal distances requires a level or a distance measuring tool, calculating angles necessitates a protractor or an angle finder, and indicating level surfaces typically involves a bubble level. Each serves its unique purpose, but only a plumb line specifically indicates vertical alignment as a direct application of gravity.