Convert from span to fermi

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

Unit Definition (fermi)
The Fermi was a metric unit of distance formerly used in atomic physics. One Fermi equals 10e-15 meter, or 1 femtometer. The unit was named after Enrico Fermi (1901-1954), the Italian-American physicist who built the first nuclear reactor.