Editing Goniometer (section)

==Protractor==
[[Image:Protractor2.jpg|thumb|right|upright=1.35|A half-circle protractor marked in degrees (180°).]]
A '''protractor''' is a [[measuring instrument]], typically made of transparent plastic, for measuring [[angle]]s. Some protractors are simple half-discs or full circles.  More advanced protractors, such as the [[#Bevel|bevel protractor]], have one or two swinging arms, which can be used to help measure the angle.

Most protractors measure angles in [[degree (angle)|degree]]s (°). Radian-scale protractors measure angles in [[radians]]. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into [[Minute and second of arc|arcminutes]]. A protractor divided in [[centiturn]]s is normally called a "[[percentage protractor]]".

===Bevel===
{{confusing|date=September 2020}}
[[File:Ocelový dílenský úhloměr.jpg|thumb|A half-circle bevel protractor]]
[[File:Universal bevel protractor.jpg|thumb|A universal bevel protractor.]]
A bevel protractor is a graduated circular protractor with one pivoted arm; used for measuring or marking off angles. Sometimes [[Vernier scale]]s are attached to give more precise readings. It has wide application in architectural and mechanical drawing, although its use is decreasing with the availability of modern drawing software or [[CAD]].

Universal bevel protractors are also used by toolmakers; as they measure angles by mechanical contact they are classed as mechanical protractors.<ref name="Magazines1993">{{cite magazine |last=Capotosto |first=Rosario |date=December 1993 |title=Bridge City Protractor |url=https://archive.org/details/bub_gb_4eMDAAAAMBAJ/page/n87/mode/2up |department=Tool Test |magazine=[[Popular Mechanics]] |page=76 |issn=0032-4558 |access-date=12 April 2020}}</ref><ref>{{cite book
 | last = Farago
 | first = Francis T
 |author2=Curtis
  | title = Handbook of Dimensional Measurement
 | publisher = Industrial Press Inc
 | year = 1994
 | pages = 580 
 | url = https://books.google.com/books?id=eVQPSr8nWekC&q=bevel+protractor+how+to+use&pg=PA255
 | isbn = 0-8311-3053-9}}</ref>

The bevel protractor is used to establish and test angles to very close tolerances. It reads to 5 arcminutes (5′ or {{sfrac|1|12}}°) and can measure angles from 0° to 450°.
  
The bevel protractor consists of a beam, a graduated dial, and a blade which is connected to a swivel plate (with Vernier scale) by a thumb nut and clamp. When the edges of the beam and blade are parallel, a small mark on the swivel plate coincides with the zero line on the graduated dial. To measure an angle between the beam and the blade of 90° or less, the reading may be obtained directly from the graduation number on the dial indicated by the mark on the swivel plate. To measure an angle of over 90°, subtract the number of degrees as indicated on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way.
  
Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved.

===Gallery===
<gallery mode=packed>
Image:Protractor1.svg|A 360° protractor marked in degrees.
Image:Grad protractor.png|A 400 gon protractor marked in [[gradian]]s.
Image:Navigational rules types.JPG|A "[[Cras navigation plotter]]" double-protractor, in foreground, named after its inventor [[Jean Cras]].
Image:Protractor_Rapporteur_Degrees_V3.jpg|A half circle protractor marked in degrees (180°).
Image:Set square Geodreieck.svg|{{lang|de|[[Geodreieck]]}}, a special type of [[protractor triangle]] (180°).
File:Electronic protractor.jpg|Electronic protractor
File:Degree-Radian Conversion.svg|Protractor scale in degrees and radians
</gallery>