Convert from shackle to mile [international]

Unit Definition (shackle)
The shackle is a traditional unit of length used for measuring the lengths of nautical cables and chains, especially anchor chains. Anchor chains are formed by using shackles to join short lengths of chain. When the anchor is dropped and the chain runs out, a seaman counting the number of shackles can report the total length of chain deployed. The size of the unit therefore varied somewhat, depending on the length of the short chains used. In Britain, the unit became standardized in the 16th century at 12.5 fathoms (75 feet or 22.86 meters). In 1949, the Royal Navy adopted a length of 15 fathoms, which is 90 feet or 27.432 meters; this brought the British shackle in line with the U.S. unit, which is usually called the shot.

Unit Definition (mile [international])
The mile is one of the most common measurements of distance. It originates from the Latin word for 1000, 'mille'. Originally a mile was the distance a Roman legion could march in 1000 paces. In medieval Britain, several mile units were used, including the modern mile defined as 8 furlongs (1609 meters). Note that French, Scottish and Irish miles varied from the English. In 1592, Parliament defined the statute mile to be 8 furlongs or 1609.344 meters.