A plumb bob, also known as a plummet, is a weight with a pointed tip on the bottom that is suspended from a string and used as a vertical reference line or plumb-line. It is a tool that has been used for thousands of years, dating back to Ancient Egypt. The plumb in plumb bob derives from Latin plumbum, which means "lead," the material that was once used for the weighted bob at the end. The plumb bob is used to find nadir, which is the local vertical direction pointing towards gravity, and in tools such as steel tape and theodolites.
A plumb bob may be in a container of water, molasses, very viscous oils, or other liquids to dampen any swinging movement, functioning as a shock absorber. It is also used by students of figure drawing to find the vertical axis through the center of gravity of their subject and lay it down on paper as a point of reference.
In The Sims video game series, the plumbob is a green diamond that floats above the selectable sim and indicates their mood.
