The
geographical mile is a unit of length determined by 1
minute of arc along the
Earth's
equator. For the 1924 International Spheroid this equalled 1855.4
metres. Any greater precision depends more on choice of standard than on more careful measurement: the length of the
equator in the
World Geodetic System WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the
International Astronomical Union standard IAU-2000 takes the
equator to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer.