It is a precursor to the spirit level and used to establish a vertical datum. Some bobs have pointed tips that can be bent by repeated use or abuse if the point on yours is bent or out of alignment, replace it. A plumb bob, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. Excavation and foundation contractors rely upon the plumb line, and constructing a chimney the tool can indicate whether a flue is running true vertical or veering off plumb. Surveyors sometimes use plumb bobs for lining up points or transferring them. The plumb line in one place can be used to sight an object in another - a pipe, for example - for plumb. Once it is hung and still, the top and bottom points can be marked and used as guides. For example, you can locate fixtures or decorations in relation to an object or surface below (or above) using the plumb line. A spirit level will also accomplish those tasks, but some jobs are much more easily done using the tool. By holding such a line and aligning it visually with a model, an artist can measure. The plumb bob is useful in establishing vertical for a wall in construction or a doorjamb when hanging a door. A plumb line is just a piece of thread with a weight attached to its end. (Note that the line must be hanging free to get an accurate reading.) The weight, or bob, is then allowed to swing freely when it stops, the point of the bob is precisely below the point at which the string is fixed above. To use the tool, the string is fixed at the point to be plumbed. Other articles where plumb line is discussed: hand tool: Plumb line, level, and square: A plumb line is a light line with a weight (plumb bob) at one end.
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