The metric and derived SI unit for *speed* is *metre per second* (^{m}/_{s}). Speed is in the term of mathematics a scalar, that is a real number. *Velocity (v)* on the other hand also has a direction wheras *v* often is expressed as a vector value or a expressed as a speed and a radian angle to specify direction. These conversions focus on the scalar speed value.

The Imperial and U.S customary system relies on *miles* and *feet* when measuring distances which reflects in the units of speed as well.

The *knot* is defined as the speed when travelling one nautical mile per hour. Knots are used in maritime and air navigation and in meteorology.

The name comes from using a *chip log* to measure the pace of a vessel at sea. This means throwing a wooden panel attached to a line behind the stern of the wessel and counting the number of knots tied on the line passing by in a certain amount of time elapsed using a 30-second sand-glass. The knots where placed at a distance of 47 feet and 3 inches making it possible to calculate the speed in nautical miles per hour or as it became called, knots.

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