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The hand is a non-SI unit of measurement of length standardized to 4 inches (101.6 mm). It is used to measure the height of horses in some English-speaking countries, including Australia, Canada, the Republic of Ireland, the United Kingdom and the United States.
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.