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 * UNITS OF MEASUREMENT - Standards in every day life**

=**1. Definition**=

The proper [|unit of measurement] is a tool to allow us to measure and organize the world - by length, volume, energy, or some other aspect of reality. Units of measurement were among the earliest tools invented by humans.


 * Measuring units standards:**
 * Metric System
 * Imperial System
 * U.S. Customary System

=**2. Metric System and history**=

Nowadays there is a global standard, The International System (SI) of units which is the modern form of the metric system. Most countries have either used the metric system for many years, or have adopted the metric system within the last 30 or 40 years except the U.S., Liberia and Burma (Myanmar). In the UK this transition is largely done, with the only two major Imperial units still in general use being the pint and the mile. The following chart shows when various countries adopted the metric system and is based on a survey conducted by [|USMA] many years ago. The chart shows the countries names at the time; some have since changed names. And, because metrication is an evolutionary process that takes place over time, any attempt to assign a single year to a country's conversion is only an approximation.



The main points to be garnered from the chart are: 1) only a few smaller countries, including some unlisted Caribbean countries heavily influenced by the U.S., have not formally adopted the use of SI 2) among countries not claiming to be metric, the U.S. is the only significant holdout

The metric system has only seven basic measures (known as units), listed in the followin table, of which the first four are in common use and the other three are mainly for technical and scientific purposes.
 * **Type of measure** || **Standard unit** || **Symbol** ||
 * length || meter || m ||
 * mass (weight) || kilogram || kg ||
 * temperature || degree Kelvin || K ||
 * time || second || s ||
 * electric current || ampere || A ||
 * amount of substance || mole || mol ||
 * luminous intensity || candela || cd ||


 * Meter**

The word "meter" is from the Greek word "metron", which means "a measure". At the time the metric system was being defined, there were two competing approaches to the definition of the length of the meter. The initial suggestion was that it be the length of "a pendulum havin a half period of one second". The alternative approach was to set it to one ten-millionth of "the length of the earth's meridian along a quadrant". Specifically, one ten-millionth of the distance from the North Pole to the equator, along the meridian running near Dunkirk in France.


 * Kilogram**

Although the kilogram is commonly used as a measure of weight, it is actually defined as a measure of mass. Weight is a measure of how heavy something is, whereas mass is a measure of the amount of matter.


 * Temperature**

Temperature is officially measure in degrees Kelvin, but in day-to-day use the Celsius system is used instead. The original metric measure of temperature was the Celsius system, where 0 degree C was set to the freezing point of water. Officially, this has ben replaced by the Kelvin system, where 0 degree K is set to absolute zero. “Celsius” is named after the Swedish astronomer [|Anders Celsius]

=**3. Imperial and US System. History**=

Aside from the metric system, there are two other main systems of measurement in use today: the **Imperial system** of measurement and the U.S.A. system of measurement. The two systems are often confused with each other and sometimes one or the other terms are used to collectively refer to both systems (in particular Europeans often use the term Imperial system to refer to either systems). However, despite the similarities between the two, they are different systems. To properly explain this relationship, one needs to consider the history behind them. Both the Imperial system and the USA system of measurement are based on the older **English units of measurement**. Prior to 1066 the English units included Anglo-Saxon measures (likely of ancient Germanic origin). After the Norman conquest (Battle of Hastings in 1066), the Normans re-introduced Roman measures, resulting in a system including ancient Anglo-Saxon measures and Roman measures. These units were standardised by the Magna Carta of 1215 and were periodically reviewed and updated (notably in 1496, 1588 and 1758). The UK Weights and Measures Act of 1824 was one such review, which not only modified the types and sizes of the units, but renamed them from the English units of measurement to the **Imperial System of Measurement**. This new standard was then introduced throughout the UK and its colonies at this time. However, the USA had become independent prior to this and consequently did not adopt the Imperial system of measurement. Instead, they had developed their own measurement standards, based on the English units system which was used throughout the States prior to independence. As a result, the older English units developed into the USA system of measurement in the USA and into the Imperial system of measurement in the UK and countries colonised by the UK.

=**4. Metric, Imperial and US measurement units**=

The following tables show some of the more common measures, and the conversion between larger and smaller units. The left hand tables show the units for the metric system while the right hand tables show for the Imperial and USA measurement systems.
 * **Metric Length** || **Imperial/US Length** ||
 * 10 millimeters = 1 centimeter || 12 inches = 1 foot ||
 * 10 centimeters = 1 decimeter || 3 feet = 1 yard ||
 * 10 decimeters = 1 meter || 22 yards = 1 chain ||
 * 10 meters = 1 decameter || 10 chains = 1 furlong ||
 * 10 decameters = 1 hectometer || 8 furlongs = 1 mile (5280 feet) ||
 * 10 hectometers = 1 kilometer (1000 meters) ||  ||

The Imperial and USA systems have the same definition of the pound and the same definition of the ounce. However, the Imperial system uses the "stone", which is not used in the USA system. = 112 pounds (UK) || 2240 pounds || = 2000 pounds ||
 * **Metric Mass** || **Imperial/US Weight** ||
 * 1000 grams = 1 kilogram || 16 ounces = 1 pound ||
 * 1000 kilograms = 1 ton || 14 pounds = 1 stone (UK) ||
 * || 8 stones (UK) = 1 hundreadweight (UK)
 * || 100 pounds = 1 hundreadweight (US) ||
 * || 20 hundreadweight (UK) = 1 ton (UK)
 * || 20 hundreadweight (US) = 1 ton (US)

In the United States the Fahrenheit system continues to be the accepted standard for non-scientific use. All other countries have adopted Celsius as the primary scale in use. Fahrenheit is sometimes used by older generations in English speaking countries, especially for measurement of higher temperatures. **Fahrenheit**  is a temperature scale named after the German-Dutch physicist [|Daniel Gabriel Fahrnheit] who proposed it in 1724. In this scale, the freezing point of water is 32 degrees Fahrenheit, and the boiling point is 212 degrees, placing the boiling and freezing points of water exactly 180 degrees apart. =**5. Conclusions : Advanteges of Metric System**=
 * Temperature**

The metric system is a relatively modern system (just over 200 years old) which has been developed based on scientific principles to meet the requirements of science and trade. As discussed above, the Imperial and USA systems have evolved without any such constraints, resulting in a complex set of measurements that fit everyday life in a simple agricultural society but which are unsuited to the requirements of science and modern trade. Consequently, the metric system offers a number of substantial advantages: **Simplicity -** The Metric system has only 7 basic measures, plus a substantial number of measures using various combinations of these base measures. The imperial system (prior to the UK converting to metric) and the USA system have over 300 different measures, of which many are ambiguous. **Ease of calculation -** All the units in the metric system are multiplied by 10 (to make larger units) or divided by 10 (to make smaller units). **International Standard -** With the exception of the USA, all major countries have converted to the metric system (although in some countries, such as the UK, the conversion to metric is not yet complete). Consequently, for any international communication (trade, science) the metric system is the most widely used and accepted. =**6. References**=

[|http://en.wikipedia.org] [|http://standards.nasa.gov] [|http://www.emints.org]