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# Protractors

A protractor is a mathematical instrument often made from clear plastic used for measuring angles in degrees such as the angles of a triangle or a hexagon. More durable and typically higher quality protractors can be made of metals such as aluminium or Stainless Steel.

### Types of Protractor

#### Semi-Circular Protractor:

This protractor has two sets of scales graduated up to 180° in opposite directions enabling angles to be read from two directions. On the base of the protractor is a midpoint mark that indicates the position of the highest point of the angle that is going to be measured or the vertex. The semi-circular protractor is used for reading, drawing and plotting angles on paper or charts. This type of protractor is commonly used in classrooms for geometry and in mechanical and engineering-related applications.

#### The Vernier Scale:

This is used on protractors to enable them to give more precise and accurate measurements. In the Vernier scale, each graduation represents 0.02 mm or 1/12 of a degree. The Vernier scale is found underneath the main degree scale and is spaced so it reads at a constant fraction of the fixed main scale.

#### Bevel Protractors:

These are able to measure through 360° by using one or two swinging arms that can help measure the angle. The construction of a bevel protractor consists of a beam, a graduated dial and a blade which is connected to a swivel plate by a thumb nut and clamp. There are variants of this design including a universal precision protractor and a precision universal Vernier protractor with a more technical design. Bevel protractors are more accurate than regular protractors as they use a Vernier scale along with a fixed scale. The fixed dial or main scale has four sections with each one graduated from 0 ° to 90 °. The Vernier scale has 24 divisions with 12 divisions on either side of 0 with each division representing 5 minutes. As with the regular protractor, the Vernier scale is bidirectional and can be read to either side. Bevel protractors are designed for making high-precision measurements and are commonly used for producing mechanical and architectural drawings and by tool makers. Bevel protractors are often ground and made from stainless steel. Some protractors have a satin chrome finish to improve the visibility of the scales.

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