Convert from cana (canna, canne) to span

Unit Definition (cana (canna, canne))
The caña (canna, canne) are traditional units of distance in Spain, Italy, and southern France, respectively. The caña varied in size, but it was most often defined as 8 palmos, which makes it the Mediterranean version of the fathom, equal to roughly 2 meters or 6.5 feet. In Italy a measuring stick is still called a canna metrica. The unit is sometimes translated to "rod" in English, but "fathom" is the proper choice.

Unit Definition (span)
Span is the width of a human hand, from the tip of the thumb to the tip of the pinky finger.