Devised by French

scientists in the late 18th

century to replace the chaotic collection of units then in use. The goal of this effort was to produce a system that did not rely on a miscellany of separate standards, and to use the decimal system rather than fractions.

To obtain a standard of length a

quadrant of the earth (one-fourth of a

circumference) was surveyed (actually only in part) along the

meridian that passes through

Paris. This distance was divided into ten million parts to become the meter (spelled metre in some countries - including France (mètre)). The definition of the meter has become more and more

precise through the years since. Currently the meter is the distance light travels in a

vacuum in 1/299 792 458 second.
The

nautical mile used in modern

navigation, in relation to which boat speeds and wind

velocities are measured (one

knot is one nautical-mile-per-hour), is defined as one minute of

latitude. A degree of latitude therefore is 60 nautical miles. The quadrant of the earth measured by the

French, being 90 degrees, measures 90x60 or 5400 nautical miles. Therefore: 5400 nautical miles exactly equal 10-million meters, or 10 000 kilometers.

The

units most commonly used from the metric system are listed below:

**m** - meter/metre, for length.
**kg** - kilogram, for mass/weight.
**t** - ton, 1000 kg.
**s** - second, for time.
**°C ** - degrees Celsius, for temperature. Water freezes at 0°C and boils at 100°C.
**m**^{2} square metre, for area.
**ha** - hectare, 10,000 m^{2}.
**l** - liter/litre, for volume. 1 l of water at 4°C weighs 1 kg.
**m**^{3} - cubic metre, 1,000 litres.
**m/s** - metres per second - for wind speeds.
**km/h** - kilometres per hour - 3.6 metres per second - for velocities of
cars/planes/bicycles/joggers
**N** - newton, for force (the force of a 1 kg weight lifted form the ground (on Earth) is about 9.82 N .. BUGGER!!)
**kPa** - kilopascal, for pressure.
**J** - joule, for energy. J=N*m.
**W** - watt, for power. 1 W = 1 J/s.

See also -

English units / Metric conversion factors