An idealized mathematical object having a rigorously straight edge which can be used to draw a line segment. Although geometric constructions are sometimes said to be performed with a ruler and compass, the term straightedge is preferable to ruler since markings on the straightedge (usually assumed to be present on a ruler) are not allowed by the classical Greek rules.
Straightedge
See also
Compass, Euclidean Tools, Geometric Construction, Geometrography, Mascheroni Construction, Polygon, Poncelet-Steiner Theorem, Ruler, Simplicity, Steiner ConstructionExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Straightedge." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Straightedge.html