Did you know that...

Do you know that the speed on the sea is counted in knots?

Knot is a unit equal to one nautical mile per hour. It is used to specify the speed of a ship, airplane or wind in meteorology.
Formerly speed was measured by a piece of wood thrown out of the board with a string wrapped around it, which had knots on it every 14 meters.
The speed was calculated by measuring time of string unravelling. Nowadays this method is replaced with electric devices or it can be calculated with GPS system.