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A sample compass correction card, showing the deviation correction for a given heading. Once the compass has been corrected using small magnets fitted in the base and with soft iron balls, any residual deviation is recorded as a table or graph: the compass correction card, which is kept on board near the compass. [6]
In navigation, the heading of a vessel or aircraft is the compass direction in which the craft's bow or nose is pointed. Note that the heading may not necessarily be the direction that the vehicle actually travels, which is known as its course or track. Any difference between the heading and course is due to the motion of the underlying medium ...
Deviation varies for every compass in the same location and depends on such factors as the magnetic field of the vessel, wristwatches, etc. The value also varies depending on the orientation of the boat. Magnets and/or iron masses can correct for deviation, so that a particular compass accurately displays magnetic bearings.
A compass rose, showing absolute bearings in degrees. In nautical navigation the absolute bearing is the clockwise angle between north and an object observed from the vessel. If the north used as reference is the true geographical north then the bearing is a true bearing whereas if the reference used is magnetic north then the bearing is a ...
Magnetic dip causes the compass to dip upward or downward depending on the latitude. Magnetic dip, dip angle, or magnetic inclination is the angle made with the horizontal by Earth's magnetic field lines. This angle varies at different points on Earth's surface. Positive values of inclination indicate that the magnetic field of Earth is ...
Dead reckoning. The navigator plots their 9 a.m. position, indicated by the triangle, and, using their course and speed, estimates their own position at 9:30 and 10 a.m. In navigation, dead reckoning is the process of calculating the current position of a moving object by using a previously determined position, or fix, and incorporating ...
Flinders bar. A Flinders bar is a vertical soft iron bar placed in a tube on the fore side of a compass binnacle. The Flinders bar is used to counteract the vertical magnetism inherent within a ship and is usually calibrated as part of the process known as swinging the compass, where deviations caused by this inherent magnetism are negated by ...
Great-circle navigation. Great-circle navigation or orthodromic navigation (related to orthodromic course; from Ancient Greek ορθός (orthós) 'right angle' and δρόμος (drómos) 'path') is the practice of navigating a vessel (a ship or aircraft) along a great circle. Such routes yield the shortest distance between two points on the globe.