Two of the units of measure most commonly used in maritime transport are "the nautical mile", to measure distance and the "knot", to measure speed. These units are also used in air navigation.

A nautical mile is equivalent to the length of one minute of arc of latitude on the surface of the earth. In meters, the nautical mile is equals to 1,852 meters; thus we see that a degree of latitude (1 degree = 60 minutes), is equal to a length of 60 nautical miles; ie 111,120 m or 111.12 km. When dealing with distances less than one nautical mile, usually, tenths of a nautical mile is used. This unit of length is not recorded in the International System of Units.

For its part, the name of "knot" is due to a system used in antiquity to measure the speed of the boats, which included a rope with knots. A knot is equal to 1,852 meters/hour, that is, 1.852 km/h. On some occasions, this unit is used by meteorologists to report on wind speeds. The "knot" is not included in the international system of units.

These two marine units are related to each other; as you can see, the value of one knot is equal to one nautical mile per hour, that is:

1 knot = 1,852 m/h = 1 nautical mile per hour