The term 'ARK UNIT' is composed of three words: 'PAIR, ' 'CUBIT, ' and 'DUO.' A PAIR is two items of the same kind, usually referring to people or animals. A CUBIT is an ancient unit of length, equal to the distance from the elbow to the tip of the middle finger, or about 18 inches. A DUO is two people or things that are closely related or work together. Therefore, the term 'ARK UNIT' can be interpreted as two people or animals working together in a space of 18 inches.