Azimuth compass
_015801.jpg")
![The azimuth is the angle formed between a reference direction (North) and a line from the observer to a point of interest projected on the same plane as the reference direction](/Images/godic/202412/22/Azimuth-Altitude_schematic.svg5801.png")
![A map showing lines of equal magnetic declination in January 2015](/Images/godic/202412/22/page1-220px-World_Magnetic_Declination_2015.pdf5801.jpg")
![An example of an azimuth compass. The visors of unequal height allow sighting of objects above the horizon.](/Images/godic/202412/22/Boussole_marine5802.png")
An azimuth compass (or azimuthal compass) is a nautical instrument used to measure the magnetic azimuth, the angle of the arc on the horizon between the direction of the sun or some other celestial object and the magnetic north. This can be compared to the true azimuth obtained by astronomical observation to determine the magnetic declination, the amount by which the reading of a ship's compass must be adjusted to obtain an accurate reading. Azimuth compasses were important in the period before development of the reliable chronometers needed to determine a vessel's exact position from astronomical observations.