Variation is not constant; it changes with every change in what?

Variation refers to the difference between true north and magnetic north, which is influenced by the Earth's magnetic field. This difference is not uniform across different locations on the Earth's surface and can change significantly as one moves geographically.

As a vessel travels from one area to another, the magnetic declination can increase or decrease depending on local magnetic anomalies. Thus, geographical location plays a crucial role in determining the variation that a mariner must consider when navigating.

In contrast, while speed, vessel heading, and cargo may impact a vessel's performance or navigation method, they do not affect the magnetic declination itself. The variation remains primarily a function of where you are on the planet, reinforcing the importance of understanding geographic influences on navigation.