Compass (drafting)

# Compass (drafting)

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Encyclopedia

A compass or pair of compasses is a technical drawing
Technical drawing
Technical drawing, also known as drafting or draughting, is the act and discipline of composing plans that visually communicate how something functions or has to be constructed.Drafting is the language of industry....

instrument that can be used for inscribing circle
Circle
A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....

s or arc
Arc (geometry)
In geometry, an arc is a closed segment of a differentiable curve in the two-dimensional plane; for example, a circular arc is a segment of the circumference of a circle...

s. As dividers, they can also be used as a tool to measure distances, in particular on map
Map
A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes....

s. Compasses can be used for mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

, drafting
Technical drawing
Technical drawing, also known as drafting or draughting, is the act and discipline of composing plans that visually communicate how something functions or has to be constructed.Drafting is the language of industry....

Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...

, and other purposes.

Compasses are usually made of metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

, and consist of two parts connected by a hinge
Hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

which can be adjusted. Typically one part has a spike at its end, and the other part a pencil
Pencil
A pencil is a writing implement or art medium usually constructed of a narrow, solid pigment core inside a protective casing. The case prevents the core from breaking, and also from marking the user’s hand during use....

, or sometimes a pen
Pen
A pen is a device used to apply ink to a surface, usually paper, for writing or drawing. Historically, reed pens, quill pens, and dip pens were used, with a nib of some sort to be dipped in the ink. Ruling pens allow precise adjustment of line width, and still find a few specialized uses, but...

. Circles can be made by fastening one leg of the compasses into the paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

with the spike, putting the pencil on the paper, and moving the pencil around while keeping the hinge on the same angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...

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, also called a dividing compass. 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.

Compass and straightedge
Compass and straightedge
Compass-and-straightedge or ruler-and-compass construction is the construction of lengths, angles, and other geometric figures using only an idealized ruler and compass....

construction is used to illustrate principles of plane geometry
Plane geometry
In mathematics, plane geometry may refer to:*Euclidean plane geometry, the geometry of plane figures,*geometry of a plane,or sometimes:*geometry of a projective plane, most commonly the real projective plane but possibly the complex projective plane, Fano plane or others;*geometry of the hyperbolic...

. 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 Elements
Euclid's Elements
Euclid's Elements is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria c. 300 BC. It is a collection of definitions, postulates , propositions , and mathematical proofs of the propositions...

) 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

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.

Scribe-compass is an instrument used by carpenters and other tradesmen. Some compasses can be used to scribe 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. The wing nut 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 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 with some accuracy.

## As a symbol

A compass is often used as a symbol of precision and discernment. As such it finds a place in logos and symbols such as the Freemasons' Square and Compasses
Square and Compasses
The Square and Compasses is the single most identifiable symbol of Freemasonry. Both the square and compasses are architect's tools and are used in Masonic ritual as emblems to teach symbolic lessons...

and in various computer icon
Computer icon
A computer icon is a pictogram displayed on a computer screen and used to navigate a computer system or mobile device. The icon itself is a small picture or symbol serving as a quick, intuitive representation of a software tool, function or a data file accessible on the system. It functions as an...

s. John Donne
John Donne
John Donne 31 March 1631), English poet, satirist, lawyer, and priest, is now considered the preeminent representative of the metaphysical poets. His works are notable for their strong and sensual style and include sonnets, love poetry, religious poems, Latin translations, epigrams, elegies, songs,...

uses the compass as a conceit
Conceit
In literature, a conceit is an extended metaphor with a complex logic that governs a poetic passage or entire poem. By juxtaposing, usurping and manipulating images and ideas in surprising ways, a conceit invites the reader into a more sophisticated understanding of an object of comparison...

in "A Valediction: Forbidding Mourning
A Valediction: Forbidding Mourning
"A Valediction: Forbidding Mourning" is a metaphysical poem written by John Donne. According to Donne's biographer Izaak Walton, Donne composed it for his wife, Anne More, in 1611, when Donne was about to embark on a trip to France and Germany...

" (1611).

• Masonic Square and Compasses
Square and Compasses
The Square and Compasses is the single most identifiable symbol of Freemasonry. Both the square and compasses are architect's tools and are used in Masonic ritual as emblems to teach symbolic lessons...

• Dividers
• Circle
Circle
A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....

• Geometrography
Geometrography
In mathematics, in geometry, geometrography is the study of geometrical constructions. The concepts and methods of geometrography were first expounded by Émile Lemoine , a French civil engineer and a mathematician, in a meeting of the French Association for the Advancement of the Sciences held at...