Straightedge
Encyclopedia
A straightedge is a tool with an edge free from curves, or straight, used for transcribing straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler
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Straightedges are used in the automotive service and machining industry to check the flatness of machined mating surfaces.
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.
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It may be used:
It may not be marked or used together with the compass
so as to transfer the length of one segment to another.
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.
Ruler
A ruler, sometimes called a rule or line gauge, is an instrument used in geometry, technical drawing, printing and engineering/building to measure distances and/or to rule straight lines...
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Straightedges are used in the automotive service and machining industry to check the flatness of machined mating surfaces.
True straightness can in some cases be checked by using a laser line level
Laser line level
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 on a surface the laser line level is laid against....
as an optical straightedge: it can illuminate an accurately straight line on a flat surface such as the edge of a plank or shelf.
Compass-and-straightedge construction
An idealized straightedge is used in compass-and-straightedge constructions in plane geometryEuclidean geometry
Euclidean geometry is a mathematical system attributed to the Alexandrian Greek mathematician Euclid, which he described in his textbook on geometry: the Elements. Euclid's method consists in assuming a small set of intuitively appealing axioms, and deducing many other propositions from these...
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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
Compass (drafting)
A compass or pair of compasses is a technical drawing instrument that can be used for inscribing circles or arcs. As dividers, they can also be used as a tool to measure distances, in particular on maps...
so as to transfer the length of one segment to another.
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.