What adjustment is made to determine the variation from true north to magnetic north?

The adjustment made to determine the variation from true north to magnetic north is known as variation. Variation refers to the difference between magnetic north (the direction that a magnetic compass points) and true north (the direction along the Earth's surface towards the North Pole). This difference is due to the irregularities in the Earth's magnetic field and can vary depending on the geographical location.

Understanding variation is crucial for pilots and navigators because it allows them to convert compass headings, which are based on magnetic north, to true headings that are more universally understood for navigation and air traffic control. Accurate navigation requires taking this variation into account to ensure safety and precision in flight operations.