What is a US Nautical Mile?
A US nautical mile is a unit of measurement used primarily in navigation and marine activities. It is defined as exactly 1,852 meters or approximately 6,076.12 feet. The term "nautical mile" originated from the need for sailors to measure distances on the Earth's surface while taking into account the curvature of the Earth.
The US nautical mile is based on the international nautical mile, which was agreed at the First International Extraordinary Hydrographic Conference in Monaco in 1929. The length was set at 1,852 meters, close to one minute of latitude. The Earth is not a perfect sphere, so a minute of latitude varies slightly with latitude, but for practical purposes the US nautical mile is a fixed value.
Speed over water is measured in knots, one knot being one nautical mile per hour, so 10 knots is 18.52km/h. The US only adopted the 1,852 meter nautical mile in 1954 – it previously used a slightly longer one.
What is a yard?
A yard is 3 feet or 36 inches. In the US you mostly see it on football fields, which run 100 yards between the goal lines, and in the UK short road distances are still signed in yards.
The yard is traditionally the distance from the nose of King Henry I of England to the thumb of his outstretched arm, though its length varied from place to place for centuries. It was only fixed internationally in 1959, at exactly 0.9144 meters.
Nearly every other country uses the meter instead. In the US, bulk soil and mulch are still sold by the cubic yard, which is 27 cubic feet.