Final answer:
The plumb bob is the tool used to ensure level, straight, and plumb installations by establishing a true vertical reference line using gravity.
Explanation:
The plumb bob is the tool used to help ensure level, straight, and plumb installations. It works by utilizing gravity to establish a true vertical reference line. When a plumb bob is suspended from a fixed point, the string it hangs from provides a precise vertical line that can help align structures accurately.
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