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.

External Protractors are instruments used on spheres to find a certain number of degrees. There are all different types of protractors, and they are used to find angles.

Protractors are included as school supplies.

Bevel Protractor

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 accurate 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.^[1]

Gallery

<gallery> Image:Protractor.jpg|A half circle protractor marked in degrees (180 degrees). Image:Protractor1.svg|A 360° protractor marked in degrees. Image:Protractor.svg|Another 360° protractor marked in degrees. </gallery>

See also

• Protractor compass
• Goniometer
• Geometry template

References

External links

• 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
• http://www.tradecombine.com/measuringinstruments/mitutoyo/miscellaneous/universalbevelprotractor.htm Picture of bevel protector.
• http://www.chandcoindia.com/products/measuring/steel_protractor.htm Different bevel protectors.
• Inspection Methods - Angular Measurement

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