I picked this up from an article a few weeks ago about the renumbering of tampa's runways.
So what makes it go back and forth?
The magnetic north pole is always slowly moving and is currently heading towards Russia from its current position in far northern Canada. The magnetic north pole moves by around 64 km (40 miles) a year because of changes within the Earth’s core (unlike the true north pole which moves very slowly due to tectonic plate movements). It has moved from extremes of around 10 degrees east in the late 16th century to 25 degrees west early in the 19th century, and is now at around 3 degrees west.
