Miles per hour
Symbol: kt or kts
The knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h.
Until the mid-19th century vessel speed at sea was measured using a chip log. This consisted of a wooden panel, weighted on one edge to float upright, and thus present substantial resistance to moving with respect to the water around it, attached by line to a reel. The chip log was "cast" over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 47 feet 3 inches (14.4018 m) passed through a sailor's fingers, while another sailor used a 30 second sandglass (28 second sandglass is the current accepted timing) to time the operation. The knot count would be reported and used in the sailing master's dead reckoning and navigation.
1kt = 0.514444m/s
1m/s = 1.943844kt