On Sep 16, 2:08 am, Ralph Jones wrote:
snip

Well, to get all pedantic, there have been several definitions of the
nautical mile, one of which was one minute of longitude at the
equator -- which has the advantage of being unambiguous since the
equator is a circle to very high precision. If you define it as a
minute of latitude you still have to specify the latitude where you
make the measurement, because the earth is not exactly spherical;
England defined it for a time as one minute of latitude measured at
the latitude of London.

Today it's simply defined as exactly 1852 meters, but "the arc length
subtended by one minute of latitude" is just peachy for navigational
purposes.

We got around to 'the arc length subtended by one minute of a great
circle' when I did a maritime navigation class back in the mid-90s.
It's a definition which is not quite correct, but resolves the
differences between lines of latitude & longitutude for this purpose.