Michael Badger's letter (Flight International, 10-16 June) demonstrates why we should not mix units of measurement. A nautical mile is one minute of latitude, not longitude, and even this varies. The claimed uniqueness of this unit is questioned by the kilometre being one ten-thousandth of 90¡ of latitude as defined by Napoleon. The derivation of any unit is unimportant compared with using a consistent system whose relationships are clearly understood.
Dr A Murray Wilson University of Sheffield, UK
Editor's reply: Michael Badger was not to blame. An error in the editing process changed "latitude" to "longitude".
Source: Flight International