Convert from button measure to fermi

Unit Definition (button measure)
The button measure is a unit of distance equal to 1/40 inch (0.635 millimeter), used to measure the thickness of buttons.

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.