Compass Definitions for Land Surveyors

compass—An instrument which indicates the direction of North and, usually, other directions with respect to North. The magnetic compass orients the direction from magnetic north; the gyroscopic compass orients the direction from astronomic north. The solar compass and the sun compass also orients the direction from astronomic north.

compass, Brunton—An instrument combining the features of both the sighting compass and the clinometer that can be used in the hand or upon a Jacob’s staff or light tripod for reading horizontal and vertical angles, for leveling, and for reading the magnetic bearing of a line. The construction of the case enables one to measure with ease the strike and dip of rock formations.

compass, lensatic—A type of compass equipped with a lens which permits the observer to read the far side of the movable dial.

compass, magnetic—An instrument having a magnetic needle to indicate magnetic north. When equipped with a sighting device and a graduated circle, it is used to determine the magnetic bearing of a line.

compass, peepsight—The sights of a compass formed by standards with slits for a sighting medium rather than a telescope.

compass, pocket—See compass, lensatic.

compass, prismatic—A small magnetic compass held in the hand when in use and equipped with peep sights and glass prism so arranged that the magnetic bearing or azimuth of a line can be read at the same time that the line is sighted over.

compass, solar—A surveyor’s compass with parts arranged to permit the instantaneous mechanical solution of the astronomic triangle (sun-­zenith-pole) and the consequent establishment of the astronomic meridian directly by observation. Originally invented for and used in the survey of the public lands of the United States, the solar compass has been replaced by the solar transit.

compass, surveyor’s—An instrument for determining the magnetic azimuth of a line of sight by means of a sighting device, a graduated horizontal circle, and a pivoted magnetic needle. The surveyor’s compass used in the early land surveys in the U.S. employed a pair of peep sights to define the line of sight and was usually mounted on a single leg, the Jacob’s staff. This instrument was displaced by the surveyor’s transit, and the solar transit.

compass bearing- See bearing.

compass rose—A circular, protractor-like device common to nautical charts enabling the navigator to obtain the directions of courses on the chart through the use of any parallel-motion instrument. Compass roses may be oriented with respect to true or to magnetic north (often both) and may be divided into either degree units or mariner’s points.

compass rule—See balancing a survey, compass rule; balancing a survey, distance prorate rule.

compass survey—See survey, compass.

Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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