Compass (drafting)
From Wikipedia, the free encyclopedia
- This article is about the drafting instrument. For other uses, see Compass (disambiguation).
A compass, also called a pair of compasses, is a technical drawing instrument that can be used for inscribing circles or arcs. It can also be used as a tool to measure distances, in particular on maps. Compasses can be used for mathematics, drafting, navigation, and other purposes.
Compasses are usually made of metal, and consist of two parts connected by a hinge which can be adjusted. Typically one part has a spike at its end, and the other part a pencil, or sometimes a pen. Circles can be made by fastening one leg of the compass into the paper with the spike, putting the pencil on the paper, and moving the pencil around while keeping the hinge on the same angle. The radius of the circle can be adjusted by changing the angle of the hinge.
Distances can be measured on a map using compasses with two spikes. The hinge is set in such a way that the distance between the spikes on the map represents a certain distance in reality, and by measuring how many times the compass fits between two points on the map the distance between those points can be calculated.
Compass and straightedge construction is used to illustrate principles of plane geometry. Although a real compass is used to draft visible illustrations, the ideal compass used in proofs is an abstract creator of perfect circles. The most rigorous definition of this abstract tool is the "collapsing compass"; having drawn a circle from a given point with a given radius, it disappears; it cannot simply be moved to another point and used to draw another circle of equal radius (unlike a real compass).
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[edit] Variants
A beam-compass is an instrument with a wooden or brass beam and sliding sockets, or cursors, for drawing and dividing circles larger than those made by a regular pair of compasses. [1]
[edit] References
- ^ This article incorporates content from the 1728 Cyclopaedia, a publication in the public domain. [1]
[edit] See also
[edit] External links
- beam or trammel compass (variant form); another example
