To understand a cable length, it is necessary to understand the other nautical terms, and their origins. Below is the unit of length for sea or nautical miles, as well as about fathoms, and cable length.

A fathom is 6 feet, the length of rope a man can extend from open arm to open arm. The rope was lowered into the sea to measure depth.

A cable length is the length of a ship's cable, about 600 feet (100 fathoms). It can be anywhere from 169 to 220 metres, depending on the standard used.

A nautical mile is 10 cable lengths, or about 6,076 feet. Today it is defined as 1,852 metres (6,076.12 feet or 1.15078 miles).

1 nautical mile = 1.1508 miles. A nautical mile is a unit of measurement used in both air and marine navigation, and for the definition of territorial waters. Historically, it was defined as one minute (1/60) of a degree of latitude. Degrees of latitude are always 60 nautical miles apart.

Despite the existence of precise modern definitions, in the early 21st century the old definitions are still in use. The Royal Yachting Association says in its manual for day skippers that "1 (minute) of Latitude = 1 sea mile", followed by "For most practical purposes distance is measured from the latitude scale, assuming that one minute of latitude equals one nautical mile", so a tenth of a nautical mile is a cable length.

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