The
metric system is a necessity when
dealing and
trading with other people. Consider that
once upon a time the
yard was measured as half the distance from finger tip to finger tip of the
King's outstreched arms, and that a
pound was the weight of "7,000 grains of
barley chosen from the middle ear". Understandably, problems arose when trading with anyone but a
friend or
neighbour.
Merchants developed their own system (the
British system) which was more accurate, but not very logical or easy to understand. Consider:
2 pints to the quart
4 quarts to the gallon
8 furlongs to the mile
12 inches to the foot
16 ounces to the pound
20 hundredweight to the ton
22 yards to the chain
Take into account that during the Middle Ages there were no less than five very different weights for the pound. This follows us through to today, as an ounce of precious metals is a different weight to an ounce of food, and an American gallon is different to a British gallon.
In 1799, following the French Revolution, standards for a metric system were set. These were:
A metre was one ten-millionth of the distance from the North Pole to the equator.
A litre was exactly 1,000 cubic centimetres.
A kilogram was the weight of one litre of water with a temperature of four degrees celsius.
While this system was definitely a step in the right direction, scientific work requires that the same measurements are able to be reproduced anywhere in the world - a fact that the system did not satisfy. An international conferance in 1875 led to the standards of length and weight in 1889, in the form of a metre ruler and a kilogram weight. These measurements are considered to be exactly correct. The weight is kept in Paris, France, and copies of these international standards were distributed throughout the world. The weight is made out of an alloy of platinum and iridium. Unfortunately, perhaps due to the cleaning processes, either the foreign weights are gaining mass or the French one is losing mass.
In 1960, an international conferance approved the International System of Units or S.I., which is explained in detail above. Also in 1960, the metre ruler was retired, and the metre was redifined in terms of light emitted from the gas krypton. This makes the system almost infinitely accurate, and you can be sure that all over the world the metric system shouldbe the same.
The people in charge of regulating all of this are called the International Bureau of Weights and Measures.