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.
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.
Compass-and-straightedge construction 
An idealized straightedge is used in compass-and-straightedge constructions in plane geometry. It may be used:
- Given two points, to draw the line connecting them.
- Given a point and a circle, to draw either tangent.
- Given two circles, to draw any of their common tangents.
It may not be marked or used together with the compass so as to transfer the length of one segment to another.
It is possible to do all compass and straightedge constructions without the straightedge. That is, it is possible, using only a compass, to find the intersection of two lines given two points on each, and to find the tangent points to circles. It is not, however, possible to do all constructions using only a straightedge. It is possible to do them with straightedge alone given one circle and its center.
See also 
- Wayne R. Moore, Foundations of Mechanical Accuracy, Moore Special Tool Company, Bridgeport, CT (1970)
External links 
Thu, 23 May 2013 06:10:10 -0700
Taking a more straightedge and upfront approach, Marc Geiger followed Patrick Moxey to give his take on what's happening now in the world of dance music. He voiced his concerns that the scene mustn't fall victim like so many others and wait till it's ...
Thu, 23 May 2013 05:08:24 -0700
“I met two of the guys in high school, but they were straightedge, so we didn't hang out until after [graduation],” Nielsen said. “Being in a beach town, [high school] was kind of weird, like for example, no one gave a fuck about the football team ...
Thu, 23 May 2013 01:53:23 -0700
With an occupancy capacity of 1,100 people, the structure has a contemporary, modular design with clean, straightedge lines aimed complementing the surrounding scenery. The mosque is similar, but smaller, to a stunning 48,000-squarefoot facility the ...
Death and Taxes
Tue, 21 May 2013 13:04:25 -0700
Grey's lyrics are the stuff of 90′s-emo dreams, exactly what made Deep Elm special for so many of us, but with a twist –he still holds very dear to his heart the pillars of a straightedge moral code. He remains proud of his roots and on this new EP ...
New Times Broward-Palm Beach (blog)
Tue, 21 May 2013 08:34:12 -0700
Turns out, even after adjusting for factors like age, sex, physical activity, and booze and cigarette consumption, current potheads had a significantly smaller waistlines than their straightedge peers. Research has shown that individuals who store fat ...
Bleeding Cool News
Mon, 20 May 2013 08:01:25 -0700
It's not that I'm some sort of superhuman, mind you, nor do I use drugs of any sort of to keep me going (I've been “straightedge” my whole life and, on top of that, haven't had caffeine in well over a decade). Again, I remain productive mainly by ...
Tue, 14 May 2013 12:17:17 -0700
Wentz and I had a nearly hour-long phone conversation in which we discussed his growing into himself, how crazy it is to be famous, and exactly how one goes from being the dude in a vegan-straightedge black-nationalist power-violence/hardcore band to ...
Mon, 13 May 2013 09:32:47 -0700
For the AP physics exam, a ruler or straightedge is allowed, but NO PROTRACTORS. • Bring a school-issued (or government-issued) photo ID. It's about time that you showed off that gorgeous school ID photo. DO NOT: • Bring a cellphone, smart phone ...
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