Knot

A knot is the unit of speed used at sea, one nautical mile per hour, where the nautical mile is 1,852 meters by international agreement. So one knot equals 1,852 meters per hour, about 0.514 meters per second or 1.151 statute miles per hour. The name comes from the old chip log, a line knotted at intervals and streamed astern for a timed run, the knots passing through the hand giving the speed. Because the nautical mile equals one minute of latitude, speed in knots ties directly to the rate of change of position in arc. The navigator uses it for log speed, speed over ground, tidal-stream rate, and the speed made good behind every ETA.