Convert from fermi to mark twain

Unit Definition (fermi)
The Fermi was a metric unit of distance formerly used in atomic physics. One Fermi equals 10e-15 meter, or 1 femtometer. The unit was named after Enrico Fermi (1901-1954), the Italian-American physicist who built the first nuclear reactor.

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.