As the building proceeded upward, the plumb line would also be taken higher, still centered on the datum. A section of the scaffolding would hold a plumb line, which was centered over a datum mark on the floor. Until the modern age, plumb bobs were used on most tall structures to provide vertical datum lines for the building measurements. The adjective plumb developed by extension, as did the noun aplomb, from the notion of "standing upright". The plumb in plumb bob derives from Latin plumbum (' lead'), the material once used for the weighted bob at the end. Etymology A plumb rule from Cassells' Carpentry and Joinery A plumb square from Cassells' Carpentry and Joinery It is used with a variety of instruments (including levels, theodolites, and steel tapes) to set the instrument exactly over a fixed survey marker or to transcribe positions onto the ground for placing a marker. It is also used in surveying, to establish the nadir with respect to gravity of a point in space. The instrument has been used since at least the time of ancient Egypt to ensure that constructions are " plumb", or vertical. If it is used for decoration, it may be made of bone or ivory. It is typically made of stone, wood, or lead, but can also be made of other metals. It is a precursor to the spirit level and used to establish a vertical datum. A plumb bobĪ plumb bob, plumb bob level, 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. For other uses, see Plumbline (disambiguation).
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