Which statement is true regarding magnetic variation?

Magnetic variation, also known as magnetic declination, refers to the angle difference between true north (geographic north) and magnetic north (the direction a magnetic compass points). This variation is not constant and changes based on geographical location. Every point on Earth has a specific magnetic variation; for example, in some areas, magnetic north may be east or west of true north, and this can shift gradually over time due to changes in the Earth's magnetic field.

Understanding this concept is crucial for navigation purposes, especially for pilots. It helps in accurately interpreting compass readings for flight planning and in-flight navigation. When pilots know the magnetic variation for their location, they can adjust their headings accordingly to ensure they are flying towards their intended destination accurately.

The other options misrepresent the nature of magnetic variation. It does not remain constant everywhere on Earth, as confirmed by the varying degrees of magnetic declination based on geographical locations. It's essential for all navigational systems, not confined only to foreign instruments, and it significantly impacts flight navigation by necessitating adjustments to heading calculations.