Convert from mark twain to meter

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 (meter)
The meter is the basic unit of length adopted under the Systeme International d'Unites (approximately 1.094 yards). The meter is also the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second by definition