Convert from twain to foot [survey]

Unit Definition (twain)
The 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 (foot [survey])
A foot (plural: feet) is a non-SI unit of distance or length, measuring around a third of a metre. There are twelve inches in one foot and three feet in one yard.