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A half-circle protractor marked in degrees (180°). A protractor is a measuring instrument, typically made of transparent plastic, for measuring angles. Some protractors are simple half-discs or full circles. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle.
The point is called 'O' ', this is the centre of the equinoctial circle- a long line F F' is drawn perpendicularly. Centre the circular protractor on O', with one line passing through P- call this XII. From A the actual hour-lines through each of the points (stars) where the protractor lines cross G,Y,P and M. [4]
Although the proposition is correct, its proofs have a long and checkered history. [1] In any case, the equivalence is why this feature is not stipulated in the definition of the ideal compass. Each construction must be mathematically exact. "Eyeballing" distances (looking at the construction and guessing at its accuracy) or using markings on a ...
The protractor head has a flat reference edge which is attached to an adjustable 180° protractor or (sometimes called a turret) with a graduated scale in both directions for reading both the angle or the complement angle. [1] The protractor head sometimes includes a small spirit level. [4] [2]
A rolling ruler can draw straight, parallel lines, and also has other instruments included, enabling it to do the jobs of a protractor and compass. [1] [2] The modern rolling ruler, with protractor, pivot pin and multiple pin holes serving as fixed length compasses has been patented in the US in 1991 by Wei Wang. [3]
Similar to the Geodreieck, a number of other protractor triangle types exist for navigation purposes. Various designs are named navigation (protractor) triangle, nautical navigational triangle, nautical set square, Portland (navigational) triangle or Portland protractor triangle, Kent-type triangle, Inoue-type A/B nautical triangle or plotting triangle, course triangle, yachtsmen triangle, and ...