Straightedges are used in the automotive service and machining industry to check the flatness of machined mating surfaces.
Straight edges are precision edges that are used to compare the straightness of an opposing surface, do precision layout, and play other supporting roles when the straightness of a surface is of concern.
A straightedge or straight edge is a tool used for drawing straight lines or checking their straightness
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.
