Convert from mark twain to arpent [France]

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.

Unit Definition (arpent [France])
The Arpent is a traditional unit of distance in French-speaking nations. It was used as a land measurement, which is the reason for 'Arpentage' becomming the French word for surveying. It has an official definition of 191.835 English feet (58.471308 meters).