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.

compass | Euclidean tools | geometric construction | geometrography | Mascheroni construction | polygon | Poncelet-Steiner theorem | ruler | simplicity | Steiner construction