SI units

International System of units, or SI in short, is a modern metric system that almost all countries use, except for Burma, Liberia and the US. Here are the units commonly used in science:

Quantity name -------->	Unit name
length-------->	metre
mass-------->	kilogram
time-------->	second
temperature-------->	kelvin

The SI was established in 1960, based on the metre-kilogram-second system, rather than the centimetre-gram-second system, which, in turn, had several variants. The SI has been declared to be an evolving system; thus prefixes and units are created and unit definitions are modified through international agreement as the technology of measurement progresses, and as the precision of measurements improves.