Straightedge

[1] 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.

It may be used: The idealized straightedge is: It may not be marked or used together with the compass so as to transfer the length of one segment to another.