Convert from furlong [survey] to X unit

Unit Definition (furlong [survey])
A furlong is a measure of distance within Imperial units and U.S. customary units. Although its definition has varied historically, in modern terms it equals 660 feet or 220 yards, and is therefore equal to 201.168 metres. There are ten chains in a furlong and eight furlongs in a mile. The name "furlong" derives from the Old English words furh (furrow) and lang (long).

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.