Wikipedia:
A cable length or cable's length 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:
International: 1⁄10 nautical mile, or 185.2 m
Imperial (Admiralty): 1⁄10 Admiralty mile, or 608 ft (185.32 m), about 101 fathoms
The traditional British fathom varied from 5½ feet to 7 feet in the Merchant
Navy.
U.S. customary (US Navy): 120 fathoms (720 feet, 219.456 m)
Fathom
fathom (abbreviation: ftm) = 6 feet or 1.8288 metres, is a unit of length in the old imperial and the U.S. customary systems, used especially for measuring the
depth of
water.
There are two yards (6 feet) in an imperial fathom.[1] Originally based on the distance between a man's outstretched arms, the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around 5–5 1⁄2 feet (1.5–1.7 m).
1 fathom =
SI units
1.82880 m 182.880 cm
US customary / Imperial units
6.00000 ft 72.0000 in
As you can see, the problems stem from
1- The difference between US and Imperial measurements
2- International Standards (IS) and US and Imperial measurements.
The same errors occur when discussing f.eks. gallons the imperial gallon is not the same as the US gallons.
A cables length is frequently used as a measurement in the UK, as is Fathom. So depending on the audience, it is natural this is used.
Just to add to the confusion:
What about Beaufort/Knots/meters per second for
wind speeds? (rough conversions: 2 x
beaufort = meters per second X 2 = knots
Of course, not to mention the metric system versus yards/feet/inches