How is magnetic variation displayed on aeronautical charts?

Magnetic variation is displayed on aeronautical charts as a value in degrees east or west of true north. This presentation helps pilots understand the difference between true north, which is based on the geographic North Pole, and magnetic north, which is where the Earth's magnetic compass points. The variation is essential for accurate navigation, as it informs pilots how much to adjust their heading to maintain the desired course considering the magnetic declination in their area.

Understanding this difference is crucial for safe and effective navigation because relying solely on the magnetic heading without accounting for the variation can lead to significant navigational errors. The indication of the variation in degrees provides a clear and precise measure that pilots can use to make the necessary adjustments for their flight path.

The other choices do not accurately represent how magnetic variation is displayed on aeronautical charts, as they refer to different concepts or are not used in aviation navigation contexts. Therefore, the presentation of magnetic variation as degrees east or west of true north is the most accurate and practical approach for aviation navigation.