Convert from cuerda to mark twain

Unit Definition (cuerda)
The Cuerda is a traditional unit of distance in Guatemala, equal to 25 varas or about 21 meters (roughly 69 feet). Since cuerda means a cord or rope in Spanish, this unit probably arose as the length of a measuring rope. The cuerda is also used as an area measure equal to 1 square cuerda or 625 square varas; this is about 440 square meters or 527 square yards. Note that the cuerda is also a traditional unit of land area in Puerto Rico, as well as a volume measurement for firewood in Cuba.

Unit Definition (mark twain)
The mark twain or twain is an old word for the number two, derived from the Anglo-Saxon twegen. The American author Samuel Clemens (1835-1910), who had been a riverboat pilot on the Mississippi in his youth, took his literary name from a traditional riverboat phrase "mark twain", meaning "exactly two" fathoms of water. This was the minimum depth needed for the boats to operate safely without running aground.