7 ms·

Also at the equator - the earth is not a perfect sphere.

• codeduck 7y ago
  No, but it's not oblate enough for the difference to cause any noticeable problems in navigation. The difference between an arc length of a minute at the equator vs a minute on the latitude scale is about 0.2% - less than the margin of error when reading a sextant.
  • pmikesell 7y ago
    What I mean is, at least in the US it is defined as an arc minute at the equator, not just any great circle.
    • codeduck 7y ago
      True; I think that's the global definition anyway.