World Magnetic Model

The World Magnetic Model (WMM) is a set of numbers and equations that is used to predict the magnetic field at any location on the Earth at a given time. The WMM is the standard model used by the US Department of Defense, the UK Ministry of Defence, and NATO. It is also used widely in civilian navigation systems. Visit the National Geophysical Data Center website for more information about the WMM.

TheoNav uses the WMM to calculate the magnetic variation at any given location on the Earth. TheoNav uses the current date from your device's system settings and assumes that you are at sea level. To calculate the magnetic variation at a different date, you must change the date and time in your system preferences.

The WMM is updated by the U.S. National Geophysical Data Center at five year intervals. To calculate magnetic variation, TheoNav uses Palm databases (.pdb files) that contains the co-efficients from different revisions of the WMM. You must install the WMM database for the correct time period for TheoNav to accurately calculate variation.

The current WMM database is:

• WMM-2025.pdb - Valid from Jan 1 2025 - Dec 31 2029

Expired databases are listed below:

• WMM-2020.pdb - Valid from Jan 1 2020 - Dec 31 2024
• WMM-2015.pdb - Valid from Jan 1 2015 - Dec 31 2019
• WMM-2010.pdb - Valid from Jan 1 2010 - Dec 31 2014
• WMM-2005.pdb - Valid from Jan 1 2005 - Dec 31 2009
• WMM-2000.pdb - Valid from Jan 1 2000 - Dec 31 2004