World Magnetic Model (WMM) Point Calculation - Magnetic Declination Estimation (outdated, uses 2014/2015 data)
WMM, World Magnetic Model
Magnetic Declination Estimation
Windows.Forms GUI (C# .NET)
Magnetic Declination in C#
MagVar.cs - Module to calculate magnetic variation and field given position, altitude, and date
wiki - Magnetic declination