Attention all points!

When I was small, I was taught at some length about the mysteries of magnetic north, about the fact that the compass needle did not point north, rather to some place a little to the west called the magnetic pole, some place in northern Canada. The difference between the two, the magnetic declination, was of the order of 7 or 8 degrees, out of a total of 360.

Ordinarily, this is not a big deal. But today we were heading north for Bellever Tor, with Laughter Tor a little to the east of it.

On the basis that the declination was 7 or 8 degrees, we headed for what turned out to be Laughter Tor. Luckily, shortly after leaving the car park, we came across a sign post which pulled us around to the west, and in due course we made it to the trig point at the top of Bellever Tor.

Rather confused, and rather cross that my map reading skills had been called into question, I thought to check. To find that in the half century since I last knew about these things, the magnetic declination had fallen to around 1 degree. Which fall is enough to account for my problem. North on the compass is now more or less north, at least in this country. Don't know about foreigns.

Also that, according to the map included above, magnetic declination is rather more complicated than the direction of some fixed point called the magnetic pole. And if you live to the south of Australia things get very complicated indeed. There must be magnetic stuff going on down in the depths that I don't know about.

I associate to the mathematics talked about in reference 4 which says that you cannot map surfaces to the unit circle in a smooth and sensible way without hitting problems. All down to something called the no retraction theorem. With amphidromic points being another geographical manifestation of this phenomenon.

PS: matters which young people, brought up on smart phones and sat nav do not need to know about?

Reference 1: https://en.wikipedia.org/wiki/Magnetic_declination. For the general idea.

Reference 2: https://www.ngdc.noaa.gov/geomag/declination.shtml. For the history. Maps of declination from the distant past to the present.

Reference 3: https://psmv2.blogspot.com/2014/10/the-quest-for-new-compass.html. The purchase of my current compass.

Reference 4: The geometry of biological time - Winfree – 1980.