Convert from shackle to pace [Roman]

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 (pace [Roman])
A pace (or double-pace) is a measure of distance used by Ancient Rome. It is the measure of a full stride from the position of the heel when it is raised from the ground to the point he heel is set down again at the end of the step. In Rome this was standardized as about five Roman feet or 58.1 English inches.