Which tool is essential for measuring vertical distances accurately in elevator installation?

A plumb bob is an essential tool for measuring vertical distances accurately during elevator installation because it operates on the principle of gravity. The weight at the end of the string provides a true vertical reference, allowing installers to determine whether structures, such as columns or walls, are perfectly vertical. This direct measurement is crucial in elevator installations, which rely on precise alignment for safety and functionality.

In contrast, while a laser level can also provide vertical measurement, it requires setup and can be affected by environmental factors like light conditions. A measuring tape is suitable for general measurements but does not ensure vertical accuracy without additional techniques. A height gauge is specialized for measuring vertical dimensions in a different context, typically in machining or metalworking, rather than construction or installation scenarios.