The bevel protractor is used to establish and test angles to very close tolerances. Universal bevel protractors are also used by toolmakers as they measure angles by mechanical contact they are classed as mechanical protractors. It has wide application in architectural and mechanical drawing, although its use is decreasing with the availability of modern drawing software or CAD. Sometimes Vernier scales are attached to give more precise readings. ( September 2020) ( Learn how and when to remove this template message)Ī half-circle bevel protractor A universal bevel protractor.Ī bevel protractor is a graduated circular protractor with one pivoted arm used for measuring or marking off angles. There might be a discussion about this on the talk page. This article may be confusing or unclear to readers. A protractor divided in centiturns is normally called a " percentage protractor". Some precision protractors further divide degrees into arcminutes. Most protractors are divided into 180 equal parts. Radian-scale protractors measure angles in radians. Most protractors measure angles in degrees (°).
More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. Some protractors are simple half-discs or full circles. Protractor A half-circle protractor marked in degrees (180°).Ī protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. The first known description of a goniometer, based on the astrolabe, was by Gemma Frisius in 1538. The protractor is a commonly used type in the fields of mechanics, engineering, and geometry. The term goniometry derives from two Greek words, γωνία ( gōnía) ' angle' and μέτρον ( métron) ' measure'. Goniometer made by Develey le Jeune in Lausanne, late 18th–early 19th centuryĪ goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. Plotting a grid using the 1:50000 scale romer on the RA Protractor.For other uses, see Goniometer (disambiguation). Read of the inner scale and plot a bearing of 4500 mils back to the trig point.Ĭhoose two points on a map and practice this procedure. To plot a backbearing from the church, turn the protractor to the left with the centre point over the church. What is the Grid Bearing from the Trig Point to the Church? The outer scale is used when plotting bearings East and inner scale for bearings West. Where the line crosses the outer scale it indicates the Grid Bearing from your position (trig point) to your target (church with tower). Then draw a line or use a plumb line to draw a line from your location (trig point) to your target (church with tower). All vertical and horizontal lines should be aligned with those on the map, overlay the centre point over your location on the map (trig point). This is the issued protractor, the metres scale romers are on the left side, these are the romers that you should use.Įnsure the map is on a flat surface, align the base line with the vertical lines on the map, the 0 should be in line with Grid North. Place the protractor over the map and align the northings and eastings with the zero lines and romer grids.
Use a line of fine cord from the centre point when plotting bearings, a plumb line.Tape up the yard scale romer to avoid mistakes.Always check the scale of the map and scale of the romer when plotting grids.The protractor should always be used when plotting grids and bearings.The British Military only use mils in navigation.