A magnetic declination is the angle between the the horizontal plane and magnetic north (direction your compass needle points) and true north (actual direction along a meridian towards the North Pole). Magnetic declination varies both from place to place as well as over time. The magnetic declination varies depending on where you are located on the Earth’s surface, and varies over time.
Magnetic Declination Calculator
Natural Resources Canada provides a free online magnetic declination calculator that can be used to calculate magnetic declination for any location and date based on the International Geomagnetic Reference Field model.