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The femtometre (American spelling femtometer, symbol fm derived from the Danish and Norwegian word femten, "fifteen"+Ancient Greek: μέτρον, metrοn, "unit of measurement") is an SI unit of length equal to 10−15 metres, which means a quadrillionth of one. This distance can also be called a fermi and was so named in honour of physicist Enrico Fermi, as it is a typical length-scale of nuclear physics.
A cable length or length of cable is a nautical unit of measure equal to one tenth of a nautical mile or approximately 100 fathoms. The unit is named after the length of a ship's anchor cable in the Age of Sail. The definition varies: