<P> The metric system is an internationally recognised decimalised system of measurement . It is in widespread use, and where it is adopted, it is the only or most common system of weights and measures . It is now known as the International System of Units (SI). It is used to measure everyday things such as the mass of a sack of flour, the height of a person, the speed of a car, and the volume of fuel in its tank . It is also used in science, industry and trade . </P> <P> In its modern form, it consists of a set of base units including metre for length, kilogram for mass, second for time and ampere for electrical current, and a few others, which together with their derived units, can measure any physical quantity . Metric system may also refer to other systems of related base and derived units defined before the middle of the 20th century, some of which are still in limited use today . </P> <P> The metric system was designed to have properties that make it easy to use and widely applicable, including units based on the natural world, decimal ratios, prefixes for multiples and sub-multiples, and a structure of base and derived units . It is also a coherent system, which means that its units do not introduce conversion factors not already present in equations relating quantities . It has a property called rationalisation that eliminates certain constants of proportionality in equations of physics . </P>

Base unit used to measure weight in the metric system
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