Magnetic Variation (MagVar) Calculator
Even a new chart may have outdated magnetic variation (declination) information shown on the compass rose. It becomes less accurate beyond five years from the year shown. The automatic MagVar map included in your GPS or chart-plotter system may have several degrees of error. You can get an up-to-date value from several sources.
An online resource can be found here: MagVar (Declination) WebApp, on the Natural Resources Canada website.
Or, you may download the app, WMM2015, which will allow you to compute the MagVar for any location without need for Internet access.
Depending on your browser, you may be asked, "Would you like to save this file?" [WMM2015.zip] If so, click 'Save File'. The file will normally be downloaded to your 'Downloads' directory. Unzip the file in a directory of your choosing. To use, click on the file WMMGUI.exe.
NOTE: This application only runs under Windows®
Depending on your version of Windows and your settings, it should open a similar window to the one shown on the left. The 'Help' feature provides clear instructions for its use. The calculated MagVar will appear in the window under 'Declination', indicated by the yellow shading.
Due to the unpredictable, changing nature of Earth's magnetic field, it is only good for the four years following the year shown on the window header. In this case, until end of 2019. A revised World Magnetic Model is due in 2020.
For Cape Breton in Summer 2017 use a value of 18°W.