League
A league is an old unit of distance that was commonly used in the past, especially for measuring distances on land or sea. Traditionally, one league equals about 3 miles or roughly 4.8 kilometers. The exact length of a league could vary by country and time period. It was often used by sailors and travelers to describe how far they had gone. Although the league is mostly obsolete today, it still appears in literature and historical contexts.
X-unit
The X-unit (symbol: xu) is a very small unit of length used primarily to measure wavelengths of X-rays and gamma rays. It was introduced in the early 20th century for precision measurements in X-ray crystallography.
1 X-unit ≈ 0.1 picometers (pm) or 10⁻¹³ meters
It allows scientists to express extremely small wavelengths typical of X-rays, which are on the order of atomic spacing
The exact definition has varied historically, but the unit remains useful for comparing wavelengths in X-ray spectroscopy and crystallography
Though largely replaced by the picometer or ångström in modern usage, the X-unit played a crucial role in early developments of atomic-scale measurement.
No conversions available for length.