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关于 Fathom
A fathom is a unit of length in the imperial and U.S. customary systems equal to 6 feet (1.8288 m), used especially for measuring the depth of water. The fathom is neither an international standard (SI) unit, nor an internationally accepted non-SI unit. Historically, it was the maritime measure of depth in the English-speaking world but, apart from within the US, charts now use metres.
来源：维基百科
