What tool is used for checking both vertical and horizontal line levels?

The spirit level is the correct tool for checking both vertical and horizontal line levels because it contains a sealed tube with a liquid, typically alcohol or hydraulic fluid, and an air bubble. When the spirit level is placed on a surface, the position of the bubble indicates whether the surface is perfectly horizontal (level) or vertical (plumb).

In practical surveying and construction applications, ensuring that structures are level is essential for stability and safety. The spirit level is a straightforward and effective device that provides immediate visual feedback, allowing surveyors and builders to make necessary adjustments to achieve the desired angles and alignments.

Other tools mentioned have specific functions that do not include checking both vertical and horizontal levels. A clinometer is specialized for measuring angles of elevation or depression. A tape measure is primarily used for measuring distance. A protractor is designed to measure angles, but it does not provide a way to check levels. Thus, the spirit level is specially designed for this purpose, making it indispensable in surveying and construction tasks.