1. What is Magnetic Variation?

Magnetic variation (also called magnetic declination) is the angle between magnetic north and true north. It varies by location and changes over time due to movements in Earth's magnetic field.

2. How Does the Calculator Work?

The calculator uses the World Magnetic Model (WMM):

Where:

• Latitude — Geographic coordinate (-90° to 90°)
• Longitude — Geographic coordinate (-180° to 180°)
• Altitude — Height above mean sea level in meters
• Date — Year for which to calculate variation

Explanation: The WMM is a joint product of NOAA and the British Geological Survey that models Earth's magnetic field and its changes over time.

3. Importance for Aviation

Details: Accurate magnetic variation is crucial for aviation navigation, allowing conversion between magnetic and true headings. Pilots must account for variation when planning flights and using magnetic compasses.

4. Using the Calculator

Tips: Enter coordinates in decimal degrees (positive for N/E, negative for S/W), altitude in meters, and the desired year. The WMM is typically valid for 5-year epochs.

5. Frequently Asked Questions (FAQ)

Q1: How often does magnetic variation change?
A: The WMM is updated every 5 years, with small annual changes. Significant variation changes may occur over decades.

Q2: What's typical variation range?
A: Varies from -20° to +20° in most populated areas, with extremes up to ±40° near magnetic poles.

Q3: Why include altitude in calculation?
A: Earth's magnetic field strength decreases with altitude, though this has minor effect on variation.

Q4: How accurate is the WMM?
A: Typically within 30 minutes of arc (0.5°) for variation, less accurate in polar regions.

Q5: When should I update my navigation data?
A: Aviation users should update navigation systems with each new WMM release (every 5 years).