<P> Before SI units were widely adopted around the world, the British systems of English units and later imperial units were used in Britain, the Commonwealth and the United States . The system came to be known as U.S. customary units in the United States and is still in use there and in a few Caribbean countries . These various systems of measurement have at times been called foot - pound - second systems after the Imperial units for length, weight and time even though the tons, hundredweights, gallons, and nautical miles, for example, are different for the U.S. units . Many Imperial units remain in use in Britain, which has officially switched to the SI system--with a few exceptions such as road signs, which are still in miles . Draught beer and cider must be sold by the imperial pint, and milk in returnable bottles can be sold by the imperial pint . Many people measure their height in feet and inches and their weight in stone and pounds, to give just a few examples . Imperial units are used in many other places, for example, in many Commonwealth countries that are considered metricated, land area is measured in acres and floor space in square feet, particularly for commercial transactions (rather than government statistics). Similarly, gasoline is sold by the gallon in many countries that are considered metricated . </P> <P> The metric system is a decimal system of measurement based on its units for length, the metre and for mass, the kilogram . It exists in several variations, with different choices of base units, though these do not affect its day - to - day use . Since the 1960s, the International System of Units (SI) is the internationally recognised metric system . Metric units of mass, length, and electricity are widely used around the world for both everyday and scientific purposes . </P> <P> The metric system features a single base unit for many physical quantities . Other quantities are derived from the standard SI units . Multiples and fractions are expressed as powers of 10 of each unit . When smaller or larger units are more convenient for given use, metric prefixes can be added to the base unit to denote its multiple by a power of ten: a thousandth (10) of a metre is a millimetre, while a thousand (10) metres is a kilometre . Unit conversions are thus always simple, so that convenient magnitudes for measurements are achieved by simply moving the decimal place: 1.234 metres is 1234 millimetres or 0.001234 kilometres . The use of fractions, such as 2 / 5 of a metre, is not prohibited, but uncommon . There is no profusion of different units with different conversion factors as in the Imperial system which uses, for example, inches, feet, yards, fathoms, and rods for length . </P> <P> The International System of Units (abbreviated as SI from the French language name Système International d'Unités) is the modern revision of the metric system . It is the world's most widely used system of units, both in everyday commerce and in science . The SI was developed in 1960 from the metre - kilogram - second (MKS) system, rather than the centimetre - gram - second (CGS) system, which, in turn, had many variants . During its development the SI also introduced several newly named units that were previously not a part of the metric system . The original SI units for the seven basic physical quantities were: </P>

A reference point from which all other measurements are made is called a(n)