Convert from league [ancient Celtic] to league [nautical]

Unit Definition (league [ancient Celtic])
League is a unit of distance long common in Europe and Latin America, although no longer an official unit in any nation.

Unit Definition (league [nautical])
The nautical league is approximately equal to three nautical miles, 1/20 degree, or 5556 meters (metres). Note that it is not equivalent to the portugese, french and spanish measurements of the league. The nautical league is also different from the league defined on land.