
1) Hand tool
Found on
https://www.crosswordclues.com/clue/straightedge

1) Rule 2) Ruler
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https://www.crosswordclues.com/clue/straightedge

A straightedge is a tool with an edge free from curves, or straight, used for transcribing straight lines, or checking the straightness of lines. If it has equally spaced markings along its length it is usually called a ruler. Straightedges are used in the automotive service and machining industry to check the flatness of machined mating surfaces....
Found on
http://en.wikipedia.org/wiki/Straightedge

• (n.) A board, or piece of wood or metal, having one edge perfectly straight, -- used to ascertain whether a line is straight or a surface even, and for drawing straight lines.
Found on
http://thinkexist.com/dictionary/meaning/straightedge/
Straight'edge` noun A board, or piece of wood or metal, having one edge perfectly straight, -- used to ascertain whether a line is straight or a surface even, and for drawing straight lines.
Found on
http://www.encyclo.co.uk/webster/S/206

[
n] - hand tool consisting of a flat rigid rectangular bar (metal or wood) that can be used to draw straight lines (or test their straightness)
Found on
http://www.webdictionary.co.uk/definition.php?query=straightedge

A length of timber or metal with at least one edge truly straight for marking out, checking levels etc.
Found on
https://www.diydata.com/general_building/building_glossary.php
noun hand tool consisting of a flat rigid rectangular bar (metal or wood) that can be used to draw straight lines (or test their straightness)
Found on
https://www.encyclo.co.uk/local/20974

a bar or strip of wood, plastic, or metal having at least one long edge of sufficiently reliable straightness for use in drawing or testing straight lines, plane surfaces, etc.
Found on
https://www.infoplease.com/dictionary/straightedge
No exact match found.