Magnetic Declination

What is Magnetic Declination?
It is the angle between True North and Magnetic North at a particular place and time on Earth. Magnetic Declination is used in sunPATH calculations so you can quickly and easily use a compass without making adjustments for the declination. Magnetic declination varies both from place to place, and with the passage of time. Due to the constant change of the declination sunPATH uses data from the National Oceanic and Atmospheric Administration (NOAA) to provide highly accurately calculations of the sun's position . NOAA updates the Magnetic Declination data every five years.
Magnetic Declination Wikipedia