Convert from league [ancient Celtic] to hair's breadth

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 (hair's breadth)
The hair's breadth is a common informal unit of distance. Human hairs vary considerably in width, depending on age, color, genetics, and other factors. An average hair is approximately 70 to 100 micrometers (µm) in diameter, so, as a rough standard, a hair's breadth is 100 µm or 0.1 millimeter (mm).