Protractor - History and Types of Protractors
The protractor is an instrument used for measuring angles. It is usually made of transparent glass or transparent plastic. Depending on the measurement system, protractor can have radian scale or degrees scale on it. The protractor is usually had semi-circle size divided into one hundred and eighty parts or full circle divided into three hundred and sixty parts.
Something that can be described as a protractor or a forerunner of a protractor is found in a tomb of an ancient Egyptian architect Kha, dating round 1400 BC (shortly before the reign of Tutankhamun).
First real protractors were made more than five hundred years ago. In a book, Briefe Description of Universal Mappes & Cardes written by Thomas Blundeville writer described a tool specifically designed for measuring angles and drawing them. The author of that book used protractors for map preparations and navigational charts for high latitude usage. Some other European mathematician also wrote about angle measurement tool at the same time, so it is not known who invented it first.
By the seventeenth century, protractors were standard tools for navigation at sea by sailors. It is also used for navigation at land. Joseph Huddart designed more sophisticated versions of protractor in 1810 for calculating ship position at sea. This protractor was named three arm protractor because it had a circular scale and three arms. Two arms are rotatable, and one central arm is fixed so protractor can set any angle relative to the center arm.
By the eighteen century protractors were widely used in geometry and mathematics, by the nineteenth century, a lot of different versions of protractors appeared and by the twentieth century the protractors became standard for school mathematics.
Types of Protractors
Protractors can be made in various shapes: most popular semi-circle, full circle, square, rectangle, sixth circles or quarter circles. Materials that protractors are made of can be wood, ivory, plastic or metal.
Protractors can be used by mechanics or engineers, but maybe the most common use are in schools, in geometry classes.
Although the protractors are made to be one-sided, that confuse new learners, so it is much easier for them to have protractors with both parties.
The first two-sided protractor was invented by Jake Adams, Musselburgh Grammar School math teacher in 2009. He named it “The Angler”.
Some of the more advanced versions of the protractors can have one or two moving arms which are helping to measure the angle such as bevel protractor. Bevel protractor sometimes have Vernier scales attached to it so it can have more precise readings. This kind of protractor are commonly used for mechanical and architectural drawing but today is more and more replaced with computer aided design or CAD.
Toolmakers are also using this protractor. Very close tolerances are possible to measure with this tool. It can read to 5 minutes or 1/12°, and any angle between 0° and 360° can be measured. Parts of a bevel protractor are a beam, a graduated dial, and a blade. The blade is connected to a swivel plate.