What is a common item that might be compared against a plumb-bob?

A plumb-bob is a tool used primarily in construction and carpentry for establishing a vertical reference line. It consists of a weighted object, typically a conical or pointed bob, suspended from a string. When the bob is still, it indicates the true vertical line due to the force of gravity.

The level is closely related to the use of a plumb-bob, as both are essential tools in ensuring structures are built straight and true. While a level indicates horizontal surfaces, a plumb-bob provides a vertical reference. When working on projects that require both horizontal and vertical components, these two tools are often used in conjunction to ensure the accuracy of measurements and alignments.

In contrast, a compass is used for navigation or drawing circles; a square is designed to create right angles; and a ruler is primarily for measuring lengths. While these tools serve important functions, they do not directly relate to the establishment of verticality like a level does in conjunction with a plumb-bob.