Nautical mile 1 sea mile", followed by "For most practical purposes distance is measured from the latitude scale, assuming that one minute of latitude equals one nautical mile". One tenth of a nautical mile is a cable length. The derived unit of speed is the knot, defined as one nautical mile per hour. The metre was originally defined as of the meridian arc from the North pole to the equator passing through Dunkirk. The Earth’s circumference is therefore approximately 40,000 km. The equatorial circumference is slightly longer than the polar circumference – the measurement based on this (40,075.017 km x x =
Nautical mile of latitude is not constant, but about at the poles and at the Equator, with a mean value of . Other countries measure the minute of arc at 45 degrees latitude, giving the nautical mile a length of . In 1929, the international nautical mile was defined by the First International Extraordinary Hydrographic Conference in Monaco as precisely 1,852 metres. Imperial units and United States customary units used a definition of the nautical mile based on the Clarke (1866) Spheroid. The United States nautical mile was defined as based in the Mendenhall Order foot of 1893. It was abandoned in