World Magnetic Model Updated

Posted by Glcc Office
 January 3, 2015

We all depend on our compasses. Even in this age of GPS which locates our positions with pinpoint accuracy and can also determine the direction of our movements, only a compass provides us our basic underlying directional information ... that is, IF we properly understand how to adjust for magnetic variance. With the earth's magnetic field always in motion, accurate adjustment requires accurate magnetic field maps. NOAA and the British Geological Survey recently completed the most current update of their World Magnetic Model (WMM). For a fascinating article on this activity that we boaters all rely on (as do our smartphones and other devices), click the chart below to check it out in Blue Water Sailing's Cruising Compass e-Zine.

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The anwer depends on the whether the supplier of the e-charts has updated to the new magnetic varience. It would prudent to wait a month or three, then obtain updated chart downloads. I downloaded the chart package for my Garmin unit, it was dated Jan 15, 2015. A quick look at the varience in local waters seems to match the varience given by the Web-based calculator for the the coordinates I entered.

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The big question is, when we are using our chart plotters for navigation, are these declinations accounted for in the magnetic headings presented as the bearing to our destination?