The metre per second became the official SI derived unit for both speed and velocity with the establishment of the International System of Units (SI) in 1960 by the
General Conference on Weights and Measures (CGPM). Prior to this, various units such as
feet per second,
miles per hour, and
knots were more commonly used, depending on the region and application. The unit derives from the SI base units of
metre (length) and
second (time), both of which were defined more precisely in the 20th century. The
metre was originally based on the dimensions of the Earth, but is now defined by the distance light travels in vacuum in 1/ of a second. The
second is defined using the vibration frequency of caesium atoms ( oscillations per second). Because of its accuracy, simplicity and preciseness, this unit is adopted as the official unit of speed and velocity and is almost always used as the unit of speed and velocity in scientific occasions. == Relation to other measures ==