Anybody who has been on the open sea without visual clues for orientation or, worse, trapped in the dark by a sudden failure of the lighting system, nknows how easy it is to feel lost. If a navigation system is available, then there is a means to calming down and finding your way. The geomagnetic declination allows one to do just that: navigate and find a way to destination with the aid of a specialized instrument called a "magnetic compass". The principle function of the compass is to indicate the North direction on a graduated horizontal disk. This disk is free to rotate around a vertical axis and is actually moved by the torque exerted by the horizontal component of the geomagnetic field on a magnet inside it. The compass indicates the direction of Magnetic North, which is different from True North. The difference between the two directions is the magnetic declination.