Finns det en förklaring till det mätningssystem som används inom flygfarten? [duplicera]

Att citera från Wikipediaartikel om ämnet:

Although the unit knot does not fit within the SI system, its retention for nautical and aviation use is important because standard nautical charts are on the Mercator projection and the scale varies with latitude. On a chart of the North Atlantic, the scale varies by a factor of two from Florida to Greenland. A single graphic scale, of the sort on many maps, would therefore be useless on such a chart. Since the length of a nautical mile, for practical purposes, is equivalent to about a minute of latitude, a distance in nautical miles on a chart can easily be measured by using dividers and the latitude scales on the sides of the chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier.[8]

e.g. BA Chart 73, Puerto de Huelva and Approaches, 2002