* International System of Units
The International System of Units (abbreviated SI from French: Système international d'unités) is the modern form of the metric system and isgenerally a system of units of measurement devised around seven base units and the convenience of the number ten. It is the world's most widely used system of measurement, both in everydaycommerce and in science. The older metric system included several groups of units. The SI was developed in 1960 from the old metre-kilogram-second system, rather than thecentimetre-gram-second system, which, in turn, had a few variants. Because the SI is not static, units are created and definitions are modified through international agreement among many nations as thetechnology of measurement progresses, and as the precision of measurements improves. The system has been nearly globally adopted. Three principal exceptions are Burma, Liberia, and the UnitedStates. The United Kingdom has officially adopted metrication, but not with the intention of replacing customary measures entirely. Canada has adopted it for all legal purposes butimperial/US units are still in use, particularly in the buildings trade.
* Imperial units
This article is about the post-1824 measures used in the British Empire and countries in the Britishsphere of influence. For the units used in England before 1824, see English units. For the system of weight, see Avoirdupois. For United States customary units, see Customary units.
Thesystem of imperial units or the imperial system is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined (until 1959) and reduced. Thesystem came into official use across the British Empire. By the late 20th century, most nations of the former empire had officially adopted the metric system as their main system of measurement.