straightedge
A straightedge or straight edge is a tool used for drawing straight lines, or checking their straightness. If it has equally spaced markings along its length, it is usually called a ruler. • Illustration — An ornate 18th century iron straightedge Straightedges are used in the automotive service and machining industry to check the flatness of machined mating surfaces. They are also used in the decorating industry for cutting and hanging wallpaper.
straightedge
Braun · Bundesarchiv, Bild 183-21314-0002 / CC-BY-SA 3.0 · This image was provided to Wikimedia Commons by the German Federal Archive (Deutsches Bundesarchiv) as part of a cooperation project. The German Federal Archive guarantees an authentic representation · CC BY-SA 3.0 de
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- physical tool · drawing instrument · mathematical instrument
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Compass-and-straightedge construction
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 pair of straightedges called winding sticks are used in woodworking to make warping easier to perceive in pieces of wood. Three straight edges can be used to test and calibrate themselves to a certain extent, however this procedure does not control twist. For accurate calibration of a straight edge, a surface plate must be used.
An idealized straightedge is used in compass-and-straightedge constructions in plane geometry. 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 • Or any of the other numerous geometric constructions The idealized straightedge is: • Infinitely long • Infinitesimally thin (i.e. point width) • Always assumed to be without graduations or marks, or the ability to mark • Able to be aligned to two points with infinite precision to draw a line through them 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 a circle and its center.
Exhibit in the Concord Museum, Concord, Massachusetts, USA.
Daderot
Ejemplo de uso de dos regles para alizar una pared.
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The biographical narrative on this page is based on the Wikipedia article Straightedge, revision 1327636165 (EN edition), by its contributors. VALÉORINE has edited that text and built its own documentary record around it. The reused material is available under CC BY-SA 4.0, and this page's reuse of it is offered under the same licence. Everything else on this page — the chronology, the holdings, the evidence, the plates and the connections — is VALÉORINE's own record. Sources and licences.
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The Encyclopedia exists whether or not anything is for sale. Corrections are recorded rather than overwritten, and every version of this record is kept. Published 14 August 2026.
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