Units and Standards (Encyclopedia of Science)
A unit of measurement is some specific quantity that has been chosen as the standard against which other measurements of the same kind are made. For example, the meter is the unit of measurement for length in the metric system. When an object is said to be 4 meters long, that means that the object is four times as long as the unit standard (1 meter).
The term standard refers to the physical object on which the unit of measurement is based. For example, for many years the standard used in measuring length in the metric system was the distance between two scratches on a platinum-iridium bar kept at the Bureau of Standards in Sèvres, France. A standard serves as a norm against which other measuring devices of the same kind are made. The meter stick in a school classroom or home is thought to be exactly one meter long because it was made from a permanent model kept at the manufacturing plant that was originally copied from the standard meter in France.
All measurements consist of two parts: a scalar (numerical) quantity and the unit designation. In the measurement 8.5 meters, the scalar quantity is 8.5 and the unit designation is meters.
The need for units and standards developed at a point in human history when people needed to know how much of something they were buying, selling, or exchanging. A farmer might want...
(The entire section is 1750 words.)
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