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in technology, angle-measuring device based on a scale of 90°. It is sometimes confused with the sextantsextant,
instrument for measuring the altitude of the sun or another celestial body; such measurements can then be used to determine the observer's geographical position or for other navigational, surveying, or astronomical applications.
, a similar instrument based on a scale of 60°. The quadrant is rarely used today.

1 In analytic geometry, one of the four regions of the plane determined by two lines, the x-axis and the y-axis. Commonly these lines are drawn perpendicular to each other, and the quadrants, or regions, they determine are numbered counterclockwise, beginning with the upper right quadrant. 2 In geometry, a region of a plane determined by two perpendicular radii of a circle and the circle itself. Thus two perpendicular diameters of a circle divide it into four regions, or quadrants.

(kwod -rănt) An instrument dating back to antiquity and used for measuring altitudes and angular separations of stars. It remained the most important astronomical instrument until the telescope was invented. It consisted of a 90° graduated arc (a quarter circle) with a swiveling arm to which a sighting mechanism was attached. In the mural quadrant the graduated arc, often very large, was attached to a wall and was orientated along the observer's meridian. The mural quadrant was therefore the forerunner of the transit circle.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

Arc of a circle, forming one-quarter of its circumference.

(religion, spiritualism, and occult)

The quadrants of a horoscope refer to four sets of three houses: Houses one, two, and three (first quadrant), houses four, five, and six (second quadrant), houses seven, eight, and nine (third quadrant), and houses ten, eleven, and twelve (fourth quadrant).

A quadrant is also an instrument used to calculate the position of celestial bodies. In Europe, quadrants superseded the use of astrolabes during the Renaissance.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

in astronomy, an astronomical angle-measuring instrument that was used to measure the altitudes of celestial bodies above the horizon and the angular separations between bodies. A quadrant consisted of a quarter-circle, whose arc was divided into degrees and fractions of a degree, usually mounted in a vertical plane. A straightedge with diopters or a viewing tube usually rotated around the axis passing through the center of the circle and situated perpendicularly to its plane. Large mural quadrants were used in the past at astronomical observatories; these were fixed to stone walls of the building. Quadrants cease to be used at the end of the 17th century.

[′kwä·drənt]
(anatomy)
One of the four regions into which the abdomen may be divided for purposes of physical diagnosis.
(electromagnetism)
(engineering)
An instrument for measuring altitudes, used, for example, in astronomy, surveying, and gunnery; employs a sight that can be moved through a graduated 90° arc.
A lever that can move through a 90° arc.
(mathematics)
A quarter of a circle; either an arc of 90° or the area bounded by such an arc and the two radii.
Any of the four regions into which the plane is divided by a pair of coordinate axes.
(mechanical engineering)
A device for converting horizontal reciprocating motion to vertical reciprocating motion.
One of the four areas between consecutive equisignal zones of a four course radio range station.
(naval architecture)
A casting, forging, or built-up frame in the shape of a sector of a circle attached to the rudder stock and through which the steering gear leads turn the rudder.
(optics)
A double-reflecting instrument for measuring angles, used primarily for measuring altitudes of celestial bodies; the instrument was replaced by the sextant.
(physiology)
A sector of one-fourth of the field of vision of one or both eyes.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

1. An angle-measuring instrument used for measuring elevations.
2. A quarter-round molding.
3. A device for fastening together the upper and lower leaves of a Dutch door.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

i. A quarter portion of a circle, centered on a NAVAID (navigational aid), oriented clock-wise from magnetic north. The divisions of the circle are as follows: NE quadrant from 000° to 089°, SE quadrant from 090° to 179°, SW quadrant from 180° to 269°, and NW quadrant from 270° to 359°.
ii. The housing in an aircraft cockpit on which the engine control lever (throttle) is mounted. The top of the quadrant is shaped like a quartercircle and, hence, the name.
iii. An instrument similar to a sextant but constructed with its arc graduated in degrees for a fourth of a circle. Often called a sextant.
v. One of the four areas between consecutive equisignal zones of a four-course radio-range station.

1. Geometry
a. a quarter of the circumference of a circle
b. the area enclosed by two perpendicular radii of a circle and its circumference
c. any of the four sections into which a plane is divided by two coordinate axes
2. a piece of a mechanism in the form of a quarter circle, esp one used as a cam or a gear sector
3. an instrument formerly used in astronomy and navigation for measuring the altitudes of stars, consisting of a graduated arc of 90? and a sighting mechanism attached to a movable arm
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
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