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A modern military compass, with included sight device for aligning. A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north.
Floating-card compass with prismatic sight (bearing 220° through eyepiece). The marine hand compass, or hand bearing compass|hand-bearing compass as it is termed in nautical use, has been used by small-boat or inshore sailors since at least the 1920s to keep a running course or to record precise bearings to landmarks on shore in order to determine position via the resection technique.
The heading indicator is arranged such that the gyro axis is used to drive the display, which consists of a circular compass card calibrated in degrees. The gyroscope is spun either electrically, or using filtered air flow from a suction pump (sometimes a pressure pump in high altitude aircraft) driven from the aircraft's engine .
Compass turns are typically performed in simulated or actual failures of the directional gyro or other navigational instruments. A magnetic compass is a simple instrument when the compass is not moving and is on the earth. A magnetic compass installed in an aircraft is subject to compass turning errors during flight.
Magnetic compass adjustment and correction is one of the subjects in the examination curriculum for a shipmaster's certificate of competency. The sources of magnetic deviation vary from compass to compass or vehicle to vehicle. However, they are independent of location, and thus the compass can be calibrated to accommodate them.
Direction determination refers to the ways in which a cardinal direction or compass point can be determined in navigation and wayfinding.The most direct method is using a compass (magnetic compass or gyrocompass), but indirect methods exist, based on the Sun path (unaided or by using a watch or sundial), the stars, and satellite navigation.
A magnetic slaving transmitter in a remote indicating compass detects the magnetic field of the Earth via a fluxgate magnetometer. A slaving control and compensator unit evaluates the data from the slaving transmitter and corrects the heading in HSI when the "slave gyro" mode is enabled.
A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically. A gyrocompass makes use of one of the seven fundamental ways to determine the heading of a vehicle. [1]