Convert from gnat's eye to league [UK nautical]

Unit Definition (gnat's eye)
The gnat's eye is an idiomatic "unit" of distance; it's common to hear that something is "as small as a gnat's eye". In fact, the eyes of typical gnats tend to have diameters similar in size to a hair's breadth: roughly 100-150 micrometers (0.10-0.15 millimeters).

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