Convert from fermi to X unit

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.

Unit Definition (X unit)
The X-unit (symbol xu) is a unit of length formerly used to measure the wavelength of X-rays and gamma rays. The X-unit is approximately 1.0021×10-13 metre. Defined by the Swedish physicist Karl Manne Georg Siegbahn (1886-1978) in 1925, the X-unit could not at that time be measured directly; the definition was instead made in terms of the spacing between planes of the calcite crystals used in the measuring apparatus.