protractor

protractor
/proh trak"teuhr, preuh-/, n.
1. a person or thing that protracts.
2. (in surveying, mathematics, etc.) an instrument having a graduated arc for plotting or measuring angles.
3. Anat. a muscle that causes a part to protrude.
[1605-15; < ML; see PROTRACT, -TOR]

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Instrument for constructing and measuring plane angles.

The simplest protractor is a semicircular disk marked in degrees from 0° to 180°. A more complex protractor, for plotting position on navigation charts, is called a three-arm protractor, or station pointer, and consists of a circular scale connected to three arms. The centre arm is fixed, while the outer two can be rotated to any desired angle relative to the centre one. A related instrument is the course protractor, which allows navigators to measure the angular distance between north and the course plotted on a navigation chart.

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▪ measurement instrument
  any of a group of instruments used to construct and measure plane angles. The simplest protractor comprises a semicircular disk graduated in degrees—from 0° to 180°. It is an ancient device that was already in use during the 13th century. At that time, European instrument makers constructed an astronomical observing device called the torquetum that was equipped with a semicircular protractor.

      A more complex form of protractor, designed for plotting the position of a ship on navigational charts, was invented in 1801 by Joseph Huddart, a U.S. naval captain. This instrument, called a three-arm protractor, or station pointer, is composed of a circular scale connected to three arms. The centre arm is fixed, while the outer two are rotatable, capable of being set at any angle relative to the centre one.

      A related instrument used by marine navigators is the course protractor. It provides an effective tool with which to measure the angular distance between magnetic north and the course plotted on a navigational chart.

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Universalium. 2010.

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Look at other dictionaries:

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  • protractor — the instrument used in geometry, is spelt or, not er …   Modern English usage

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