The league is a ancient unit of length that doesn't below to a unit system. Its symbol is simply - league.
It was originally an ancient Celtic unit as well as being common in Latin America and meant the distance "a person could walk in an hour". It is no longer a recognised unit in any nation.
Once it started to be quantified, in Argentina (legua) it represented 5.572 km, in England it was quantified as 3 miles and at sea a league is 3 nautical miles (3.452 miles).
The caliber is a unit of length based on the inch (imperial units) and uses the symbol cl.
It represents the internal diameter of a gun barrel and therefore more often than not, the size of the ammunition or round that gun requires to fire.
It is not always represented or converted exactly in inches so a table or "well-known" conversions are often used to depict measurements / ammo types instead.