Convert from mark twain to toise

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 (toise)
A linear measure used by the French in the old regime. A toise is equal to 76.71 English inches, 6.39 English feet or 1.9490 meters.