A straightedge is a tool with an accurately straight edge used for drawing or cutting straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler. A ruler, or rule, is an instrument used in Geometry, Technical drawing and engineering/building to measure distances and/or to rule straight
True straightness can in some cases be checked by using a laser line level as an optical straightedge: it can illuminate an accurately straight line on a flat surface such as the edge of a plank or shelf. A laser line level is a tool combining a Spirit level and/or Plumb bob with a Laser to display an accurately horizontal or vertical illuminated line
Compass-and-straightedge construction
An idealized straightedge is used in compass-and-straightedge constructions in plane geometry. Pentagon constructgif|thumb|right|Construction of a regular pentagon]] Compass-and-straightedge or ruler-and-compass construction is the construction of lengths or Angles Euclidean geometry is a mathematical system attributed to the Greek Mathematician Euclid of Alexandria. It may be used:
- Given two points, to draw the line connecting them.
- Given a point and a circle, to draw either tangent.
- Given two circles, to draw any of their common tangents.
It may not be marked or used together with the compass so as to transfer the length of one segment to another. A compass or pair of compasses is a Technical drawing instrument that can be used for inscribing Circles or arcs They can also be used as
It is possible to do all compass and straightedge constructions without the straightedge. That is, it is possible, using only a compass, to find the intersection of two lines given two points on each, and to find the tangent points to circles. It is not, however, possible to do all constructions using only a straightedge. It is possible to do them with straightedge alone given one circle and its center.
References
- Wayne R. Moore, Foundations of Mechanical Accuracy, Moore Special Tool Company, Bridgeport, CT (1970)
External links
Dictionary
straightedge
-adjective
- Living one's life against/without the use of alcohol, smoking, and illegal drugs.
-noun
- A tool which is flat, rectangular and commonly made of wood, metal or plastic and is used to draw, cut or check the straightness of straight lines.
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