The basic units of measurement for navigation are degrees and minutes of latitude and longitude. The basic units for Longitude are also in degrees, minutes and seconds but in the case of Longitude, there are 180 degrees, measured Eastwards or Westwards from the Meridian passing through Greenwich and expressed either as East or West. As a result, any position on the Earth can be uniquely identified in terms of Latitude and Longitude. Navigation is simply the art of calculation of the angle and the distance between any two positions. The unit of distance used in Navigation is the Nautical Mile. The definition of one Nautical Mile is taken as the length of one minute of Difference in Longitude (D.Long) at the Equator, so the hypoteneuse of the triangle is also going to be in units of minutes.