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The x unit (symbol xu) is a unit of length approximately equal to 0.1 pm (10−13 m). It is used to quote the wavelength of X-rays and gamma rays.
The barleycorn is a small English unit of length equal to 1⁄3 of an inch (i.e., close to 0.8467 cm) still used in Great Britain and Ireland as a determiner of shoe sizes.