Convert from yottameter to mark twain

Unit Definition (yottameter)
The yottametre (or yottameter), symbol: Ym, is a unit of distance. One yottametre is equal to 1x10+24 (1e+24) in scientific notation. Which is a very large distance. Note this is different from a yoctometre, which is 1e-24, a very small distance.

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.