In geometry, a protractor is a circular or semicircular tool for measuring an angle or a circle. The units of measurement utilized are usually degrees.
Some protractors are simple half-discs; these have existed since ancient times. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle.
A bevel protractor is a graduated circular protractor having a pivoted arm; used for measuring or marking off angles. Sometimes vernier scales are attached to give more precise readings. It has wide application in architectural and mechanical drawing although with the availability of modern drawing software or CAD the tool is less commonly used in that sphere.
Universal bevel protractors are also used by toolmakers, as they measure angles by mechanical contact they are classed as mechanical protractors.
A 400g protractor marked in grads.
- ^ Hearst Magazines (December 1993). Popular Mechanics. Hearst Magazines. pp. 76â€“. ISSN 00324558. http://books.google.com/books?id=4eMDAAAAMBAJ&pg=PA76. Retrieved 7 July 2011.
- ^ Farago, Francis T; Curtis (1994). Handbook of Dimensional Measurement. Industrial Press Inc. pp. 580. ISBN 0831130539. http://books.google.co.uk/books?id=eVQPSr8nWekC&pg=PA255&lpg=PA255&dq=bevel+protractor+how+to+use&source=web&ots=5YQqaa7UOT&sig=6Ey33U8eNRPiBBYQe32nsoPyryQ&hl=en#PPA253,M1.
|Wikimedia Commons has media related to: Protractors|
- Printable protractor for downloadPDF (38.8 KiB)
- More printable protractors
- How to measure angles with a protractor An interactive animation
- How to draw angles with a protractor An interactive animation
- Angle definition pages with interactive applets that are also useful in a classroom setting. Math Open Reference
-  Picture of bevel protractor.
-  Different bevel protractors.
- Inspection Methods – Angular Measurement
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This information originally retrieved from http://en.wikipedia.org/wiki/Protractor
on Wednesday 27th July 2011 1:13 pm EDT
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