What is the East-West deviation of the earth's magnetic field known as?

The East-West deviation of the earth's magnetic field is known as magnetic variation. This term refers specifically to the angular difference between true north (geographic north) and magnetic north, which can vary from place to place. Understanding this concept is crucial for navigation and compass usage, as it helps in converting compass readings into true direction.

Magnetic variation can change not only based on geographical location but also over time due to fluctuations in the Earth's magnetic field. This variation is essential for navigators in order to correct their bearings, ensuring accurate course plotting.

The other terms, while related in the context of magnetism, do not specifically refer to the East-West aspect of the magnetic field. For instance, magnetic declination is often synonymous with magnetic variation, but it is commonly used in a more formal sense to describe the angular difference specifically. Geomagnetic anomaly refers to deviations from the expected magnetic field strength in a given area due to geological structures and is not centered on the East-West deviation itself. Magnetic inclination, on the other hand, describes the angle of magnetic field lines relative to the Earth's surface, representing the North-South component rather than the East-West deviation.