RK Henry writes:

Except that apparently true north DOES move. The tsunami/earthquake of
a year and a half ago reportedly caused the north pole to shift about
an inch as well as decreasing the length of a day. Just goes to show,
you can't depend on anything.

All earthquakes cause such effects. However, if they produce changes
that are below the resolution threshold of avionics, they aren't a
problem. The magnetic pole, on the other hand, moves perceptibly over
time--enough to require new charts and new regulation of stations and
instruments.

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