View source for Compass (drawing tool)

{{Short description|Drafting instrument}}
{{about|the drafting instrument||Compass (disambiguation)}}
{{More citations needed|date=November 2023}}
[[File:Zirkel.jpg|thumb|A beam compass and a regular compass]]
[[File:IMB DQj3Fs.gif|thumb|Using a compass]]
[[File:Cyrkiel RB1.jpg|thumb|upright|A compass with an extension accessory for larger circles]]
[[File:Rotring S0214750 with Rapidograph 0.5 mm drawing 1.5–15 mm circles.jpg|thumb|upright|A bow compass capable of drawing the smallest possible circles]]

A '''compass''', also commonly known as a '''pair of compasses''', is a [[technical drawing]] instrument that can be used for inscribing [[circle]]s or [[Arc (geometry)|arcs]]. As [[caliper#Divider caliper|dividers]], it can also be used as a tool to mark out distances, in particular, on [[map]]s. Compasses can be used for [[mathematics]], [[technical drawing|drafting]], [[navigation]] and other purposes.

Prior to computerization, compasses and other tools for manual drafting were often packaged as a set<ref>[http://www.engineersupply.com/alvin-speed-bow-compass-set-366s.aspx a current vendor's product]</ref> with [[interchangeable parts]]. By the mid-twentieth century, [[Technical drawing tool#Templates|circle templates]] supplemented the use of compasses.{{Citation needed|date=February 2021}} Today those facilities are more often provided by [[computer-aided design]] programs, so the physical tools serve mainly a didactic purpose in teaching [[geometry]], [[technical drawing]], etc.

==Construction and parts==
Compasses are usually made of metal or plastic, and consist of two "legs" connected by a [[hinge]] which can be adjusted to allow changing of the [[radius]] of the circle drawn. Typically one leg has a spike at its end for anchoring, and the other leg holds a drawing tool, such as a [[pencil]], a short length of just pencil lead or sometimes a [[pen]].

===Handle===
The handle, a small knurled rod above the hinge, is usually about half an inch long. Users can grip it between their pointer finger and thumb.

===Legs===
There are two types of leg in a pair of compasses: the straight or the steady leg and the adjustable one. Each has a separate purpose; the steady leg serves as the basis or support for the needle point, while the adjustable leg can be altered in order to draw different sizes of circles.

===Hinge===
The screw through the hinge holds the two legs in position. The hinge can be adjusted, depending on desired stiffness; the tighter the hinge-screw, the more accurate the compass's performance. The better quality compass, made of plated metal, is able to be finely adjusted via a small, serrated wheel usually set between the legs  (see the "using a compass" animation shown above) and it has a (dangerously powerful) spring encompassing the hinge. This sort of compass is often known as a "pair of Spring-Bow Compasses".

===Needle point===
The needle point is located on the steady leg, and serves as the center point of the circle that is about to be drawn.

===Pencil lead===
The pencil lead draws the circle on a particular paper or material. Alternatively, an ink [[Nib (pen)|nib]] or attachment with a [[technical pen]] may be used. The better quality compass, made of metal, has its piece of pencil lead specially sharpened to a "chisel edge" shape, rather than to a point.

===Adjusting nut===
This holds the pencil lead or pen in place.

==Uses==

Circles can be made by pushing one leg of the compasses into the [[paper]] with the spike, putting the pencil on the paper, and moving the pencil around while keeping the legs at the same [[angle]]. Some people who find this action difficult often hold the compasses still and move the paper round instead. The [[radius]] of the intended circle can be changed by adjusting the initial angle between the two legs.

Distances can be measured on a map using compasses with two spikes, also called a [[dividers|dividing compass]] (or just "dividers"). 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 compasses fit between two points on the map the distance between those points can be calculated.

==Compasses and straightedge==
[[Compass-and-straightedge construction|Compasses-and-straightedge constructions]] are used to illustrate principles of [[plane geometry]]. Although a real pair of compasses 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 pair of compasses). [[Euclid]] showed in his second proposition (Book I of the ''[[Euclid's Elements|Elements]]'') that such a collapsing compass could be used to transfer a distance, proving that a collapsing compass could do anything a real compass can do.

==Variants==
A '''[[beam compass]]''' is an instrument, with a wooden or brass beam and sliding sockets, cursors or trammels, for drawing and dividing circles larger than those made by a regular pair of compasses.<ref>{{1728 |title= Beam-Compasses}}</ref><!-- {{ref label|1728|1|^}} -->

'''Scribe-compasses'''<ref>Fine Woodworking, Build a Fireplace Mantel, Mario Rodriquez, pgs. 73, 75, The Taunton Press, No. 184, June 2006</ref> is an instrument used by carpenters and other tradesmen. Some compasses can be used to draw circles, bisect angles and, in this case, to trace a line. It is the compass in the most simple form. Both branches are crimped metal. One branch has a pencil sleeve while the other branch is crimped with a fine point protruding from the end. A wing nut on the hinge serves two purposes: first it tightens the pencil and secondly it locks in the desired distance when the wing nut is turned clockwise.

'''Loose leg wing dividers'''<ref>The Carpenter's Manifesto, Jeffrey Ehrlich & Marc Mannheimer, Holt, Rhinehart & Winston, pg. 64, 1977</ref>  are made of all forged steel. The pencil holder, thumb screws, brass pivot and branches are all well built. They are used for scribing circles and stepping off repetitive measurements<ref>Fine Woodworking, Laying out dovetails, Chris Gochnour, pg. 31, The Taunton Press, No. 190, April 2007</ref> with some accuracy.

A '''[[reduction compass]]''' or '''proportional dividers''' is used to reduce or enlarge patterns while conserving angles.

'''Ellipse drawing compasses''' are used to draw ellipse.
{{Gallery
  |title=Compass variants
  |align=center
  |File:Beam Compass.jpg|Keuffel & Esser Arrow [[beam compass]] set for drafting.
  |File:Ellipse compass-MHS 614-IMG 3827-gradient.jpg|18th-century [[Trammel of Archimedes|ellipse-drawing compass]] ([[Musée d'histoire des sciences de la Ville de Genève|MHS Geneva]])
  |File:Reduction compass-MHS 1880-IMG 3829-gradient.jpg|Simple [[reduction compass]] ([[Musée d'histoire des sciences de la Ville de Genève|MHS Geneva]]).
  |File:Reduction compass-MHS 1914-IMG 3834-gradient.jpg|Sliding-pivot [[reduction compass]] by Nairne on London, 18th century ([[Musée d'histoire des sciences de la Ville de Genève|MHS Geneva]]).
}}

== As a symbol ==
[[File:Nuvola apps designer.svg|thumb|75px|A computer drawn compass, used to symbolize precise designing of applications.]]

A pair of compasses is often used as a symbol of precision and discernment. As such it finds a place in logos and symbols such as the [[Freemason]]s' [[Square and Compasses]] and in various [[computer icon]]s. English poet [[John Donne]] used the compass as a [[conceit]] in "[[A Valediction: Forbidding Mourning]]" (1611).
<gallery>
File:Scribe line A.jpg|Compass for tracing a line.
File:Scribe compass A.jpg|Flat branch, pivot wing nut, pencil sleeve branch of the scribe-compass.
File:Loose leg wing dividers.jpg|6 inch (15&nbsp;cm) dividers made from forged steel.
File:Compas de proportion 1.jpg|One type of sector.
File:Coat of arms of East Germany (1955–1990).svg|A compass on the former [[Coat of arms of East Germany|National Emblem of East Germany]] (former German Democratic Republic).
File:Masonic silver pendant.jpg|The compass is a [[Square and Compasses|Masonic symbol]] that appears on jewellery such as this pendant.
</gallery>

== See also ==
{{Portal|Mathematics}}
* [[Caliper#Divider caliper|Dividers]]
* [[Circle]]
* [[Geometrography]]
* Masonic [[Square and Compasses]]
* [[Technical drawing tools]]

==References==
<references />
<!-- #{{note label|1728|1|^}} {{1728}} [http://digicoll.library.wisc.edu/cgi-bin/HistSciTech/HistSciTech-idx?type=turn&entity=HistSciTech000900240243&isize=L]
# Fine Woodworking, Build a Fireplace Mantel, Mario Rodriquez, pp. 73, 75, The Taunton Press, No. 184, June 2006
# The Carpenter's Manifesto, Jeffrey Ehrlich & Marc Mannheimer, Holt, Rhinehart & Winston, p. 64, 1977
# Fine Woodworking, Laying out dovetails, Chris Gochnour, p. 31, The Taunton Press, No. 190, April 2007
 -->

==External links==
{{Commons and category|Compass (drafting)|Compass_(drafting)}}
* [https://web.archive.org/web/20160603123800/http://museum.nist.gov/object.asp?ObjID=9 Beam or trammel compass] (variant form)

{{Measuring and alignment tools}}
{{Authority control}}

[[Category:Mathematical tools]]
[[Category:Navigational equipment]]
[[Category:Stonemasonry tools]]
[[Category:Technical drawing tools]]