Currently Marble only supports two measurement units: miles and km. For aviation and navigation there is another relevant unit:  nautical miles. See:

http://en.wikipedia.org/wiki/Nautical_mile

In Marble the measure system is covered in a consistent way. Internally Marble does the whole calculation in meters/kilometers. Using that and the constants KM2MI and MI2KM inside lib/marble/MarbleGlobal.h all the values are adjusted inside the view and plugins on the fly.

So this task includes:

• introducing NM2KM and KM2NM inside lib/marble/MarbleGlobal.h
• adding the necessary conversion code in the whole Marble code base. Just do a grep -r -i  "km2mi" * and a grep -r -i  "mi2km" * in the root directory of the marble source code to find all occurences and adjust the code in each place.
• Add the proper text to the settings dialog
• Do testing