The nautical knot finds its origin in a clever method; sailors once used to measure their speed at sea. In shipping, the term knot (kn) is used to measure the speed of a ship. It is a unit of speed, which is equivalent to the velocity at which 1 nautical mile is travelled in 1 hour. The term knot dates from the 17th century when sailors measured the speed of their ship by using a device called a "common log." For measurement purposes, 1 knot (kn) = 6076 ft/hour and 1 nautical mile are equal to 1.2 mi/hour.