- Plumb-bob
A plumb-bob or 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.
This instrument has been used since the time of the ancient Egyptians by bricklayers, masons, and carpenters to ensure that their constructions are "plumb", or perfectly upright. It may also be used in
surveying to sight a point on the ground that is not readily visible. Small plumb bobs are included in the kits of various instruments such as levels andtheodolite s. They are used to set the instrument exactly over a fixed datum marker, prior to taking fresh readings.Fact|date=May 2008Etymology of the name
The "plumb" in the name "plumb-bob" comes from the fact that such tools were archetypically made of
lead (Latin ""). The adjective "plumb" developed by extension.Use
Up until the modern age, on most tall structures, plumb-bobs were used to provide vertical datum lines for the building measurements. A section of the scaffolding would hold a plumb line that was centered over a datum mark on the floor. As the building proceeded upwards the plumb line would also be taken higher, still centered on the datum. Many cathedral
spire s,domes andtower s still have brass datum marks inlaid into their floors, that signify the center of the structure above.Fact|date=May 2008The early skyscrapers used heavy plumb-bobs hung on wire in their lift wells. The weight would hang in a container of oil to dampen any swinging movement, functioning as a
shock absorber .Fact|date=May 2008Often,
figure drawing students will also make use of a plumb line to find the vertical axis through thecenter of gravity of their subject and lay it down on paper as a point of reference. The device used may be purpose-made plumb lines, or simply makeshift devices made from a piece of string and a weighted object, such as ametal washer . This plumb line is important for lining up anatomical geometries and visualizing the subject'scenter of balance .Fact|date=May 2008References
* [http://www.antiquetools.com/10-tools/10-Tools/Plumb-Bob.html 60 oz. Plumb Bob] .
* [http://www.builderbill-diy-help.com/string-line.html String Line and Plumb Bob] .
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