Mile two points on the navigational chart, then place the open dividers against the minutes-of-latitude scale at the edge of the chart, and read off the distance in nautical miles. The Earth is not perfectly spherical but an oblate spheroid, so the length of a minute of latitude increases by 1% from the equator to the poles. Using the WGS84 ellipsoid, the commonly accepted Earth model for many purposes today, one minute of latitude at the WGS84 equator is 6,046 feet and at the poles is 6,107.5 feet. The average is about 6,076 feet (about 1,852 metres or 1.15 statute miles).
Nautical almanac miles the position line is from the trial position. Nautical almanac A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for each whole hour of the year the position on the Earth's surface (in declination and Greenwich hour angle) at which the sun, moon, planets and first point of Aries is directly overhead. The positions of 57 selected stars are specified relative to the first point of Aries. In Great Britain,