straightedge

In geometry and technical drawing, a straightedge is a rigid, straight edge used to draw lines. It is typically a ruler without measurement marks, and it is used with a compass to perform classical straightedge-and-compass constructions. The straightedge provides an exact line through given points, but it does not itself measure distances or angles.

In classical drafting and geometry, the combination of a straightedge and a compass enables many constructions that Euclid described, such as drawing a line through two points, or locating intersections of lines and circles. A straightedge is characterized by its lack of calibrated scale; it is the instrument that enforces straightness rather than scale. In some mathematical treatments, a straightedge is abstracted as an entity that can create lines between points without measurement.

Straight edge may also refer to the Straight Edge movement, a lifestyle and subculture prominent in the 1980s and onward. Adherents advocate abstinence from alcohol, illegal drugs, and, in some circles, tobacco and promiscuity. The movement originated in the punk and hardcore scenes in the United States and the United Kingdom, and it has no central authority. Practices and beliefs vary among individuals and groups, and the term is used to identify a wide range of adherents, from core members to occasional supporters.