What is a magnetic declination

The declination correction

When navigating with a map and compass, one must be aware that true north (i.e. the north pole) does not coincide with magnetic north. The angle between true and magnetic north is called the declination and is east or west of magnetic north, depending on where you are on earth.

With an easterly declination, the earth's magnetic field points in a direction that passes east of the North Pole. A western declination corresponds to a deviation in the west. In many parts of the world, the declination is so low that it doesn't need to be taken into account when navigating outdoors. In some places, however, the declination is considerable and must be taken into account at all times for precise navigation.

Always check the local declination before you start navigating. The angle of declination changes over time due to the fluctuation of the earth's magnetic field.

Many Suunto compasses offer fixed or adjustable declination correction. The fixed declination correction is an additional scale under the compass needle. To use it, you must first determine the direction with the protractor and then turn until the compass needle points to the declination scale according to the local declination. This is necessary every time you read the compass.

The adjustable declination correction is set once at the beginning of the navigation. To do this, turn the north arrow on the bottom of the can to the angle that corresponds to your local declination. The compasses are equipped with a small screwdriver and a printed declination scale to make this adjustment easier.

After setting the correct declination, the compass can be used regardless of the declination until you reach a new location with a different declination.

There is also a third north called the grid north. Depending on whether you are on the central meridian of the map or on its eastern or western edge, it can show a directional deviation from the geographic North Pole. If so, the map has a description of that perspective error and declination information. When navigating outdoors, landmarks are often found, so that this effect can be ignored.

In addition to the declination, other phenomena can have an influence on the direction in which a compass points. The ground can contain magnetic minerals such as magnetite, which can have a strong influence on the compass. It is important that you regularly review your progress on the map so that you can correct any discrepancies due to such minerals.

Power lines and other human structures can also influence the compass information. Crossing bridges or underground lines, and even working on a surface that contains nails, can temporarily skew the compass result. Magnetic materials or objects that you carry with you can also affect your compass.

When using a compass, always pay attention to what you have with you and what is around you. Keep your distance from possible disruptive factors in order to achieve a good result.