Knot (nautical)
A knot is a unit of speed equal to one nautical mile per hour. It is 1852 metres per hour precisely (approx 1.15 mph or 0.5144 m/s).
The knot is widely used in air and sea navigation.
In some sailing ships, speed was measured by casting the log from the stern. The log was relatively immobile, and attached by line to a reel. Knots placed at a distance of 47 feet 3 inches (14.4018 m) passed through a sailor's fingers, while another used a 28 second sandglass to time the operation. The knot count would be reported and used in the sailing master's dead reckoning and navigation.
Since a knot is a measure of speed, the expression "knots per hour" is a solecism. Taken literally (nautical mile/hour²), it would be a measure of acceleration.
Terms
KTAS stands for "knots true airspeed". It is a measure of an aircraft's true airspeed through the air. Similarly, KIAS is "knots indicated airspeed", meaning the airspeed shown on the airspeed indicator, KCAS is "knots calibrated airspeed", or indicated airspeed corrected for position error, and KEAS is "knots equivalent airspeed", which is calibrated airspeed corrected for compressibility effects.
