Little is known about the occurrence of measuring instruments. The earliest written sources are found on the territory between the rivers Tigris and Euphrates containing data units. Arose from the need to measure the distance, the weight of the different products, the amount of water and other liquids, times, etc., the measures of length, mass, volume, etc. represented in all units that were based on different parts of the body. Thus, elbow, hand, human foot, which were the very first means measuring system formed the basis for action. For example, there have been ancient Egyptian elbow, the elbow Persian elbow Babylon; Greece - foot and leg ancient Olympic, and in Western Europe - Roman foot, leg and foot ancient Olympic.

To measure the weight of primitive man used units determined based on a number of grains of wheat, barley, rice or lambs. This way of assessing the weight found in all regions of the ancient world, both in the East (Babylon, Egypt, etc.) and in Greece, the Roman Empire, etc. With the advent scales, grains are used as weights. Many units were taken over by Roman civilization of Western Europe, but the fall of the Roman Empire led to diversification which led to much confusion. Emperor Charlemagne tried by decree unification of units in all countries united under the crown, but the attempt failed with his Empire.

Development of a new company, with the birth since the 14th century, some major cities and employed in France, Germany, Italy and other European countries and developing an economy based on manufacturing and agriculture, who helped establishment of trade relations land and sea - all these constituted a strong incentive for the development of theoretical science - mathematics, astronomy, mechanics, and applied sciences. Then there is an imperative and the use of unique units, included in the "measures" and "weights" for quantitative expression of the values of physical quantities both within each country and the economic and cultural relations between them. In the first half of the 19th century was imposed with absolute necessity, unification of units, as it was required in the countries of Western Europe, primarily in France after the revolution of 1789. Despite attempts to unify units of measure taken by the French government has failed to require the use of the same units throughout France. Throughout Europe and other continents continue to have a wide variety of measures, which was to be treated with uncertainty and confusion measurements made with them. Comparison of steps, referred to as the "Paris", the action for the same size used in England, carried out by a group of scientists in 1742, has led, for example, to the conclusion that between the units of length pied or foot, and units of mass pounds or pound, there are differences of 6% and 8% respectively. Constituent National Assembly (France) adopted on 26 March 1791, the principle of establishing a system of measures based on the unit length, referred to meter equal to the 10-millionth part of the quarter meridian earth. " This definition has been proposed by a committee appointed by the Academy of Sciences in Paris, which was composed by the following scientists: Borda, Lagrange, Laplace and Monge. 66 units of area and volume history of physical units and technologies, vol. 7, no. 1-2, 2009 would be equal in value to decimal multiples and multiples of square meters, respectively, of the cubic meter.

French National Assembly adopted also on 6 March 1891 and the judgment unit mass to be the mass of a cubic decimetre of water at the maximum density, at 4 C. Based on the results of measurements of the meridian arc and Barcelona Dunkuerque made by Delambre and Mechain, it was made a standard platinum meter of landmarks. Based on the results of the measurements made by Lavoisier and his collaborators on the weight of a known volume of water it was made a standard kilogram of platinum. The two platinum standards, the meter and the kilogram were made at June 22, 1799, Archives of the French Republic, received the name meters from the Archives and respectively Kilogram of the Archives. Starting from the meter and kilogram units, they may form decimal multiples and sub-multiples, by adding prefixes mil (1/1000) cents (1/100), therefore, (1/10), respectively, kilo (1000), hecto ( 100), deca (10) to the meter and gram names (for exempu millimeter or kilogram). As the system units created in France was based on meter unit, he was called metric. Then began a new stage in the history of units, a step that would lead to the International System of Units (SI) .

In the first half of the century. XIX, followed the introduction of new units in France and their recognition by other countries. Obviously, this procedure was difficult, due in the first place, the power of the old habits of action and, secondly, some differences in the definition of metric and determining the length of the unit kilogram weight of a cubic decimetre of water. However, the progressive nature of Metric System ensures the removal of any differences that arise. Basic incentive was the idea of internationalization. This idea became even more topical with the advent of machinery and equipment, railways have developed considerable international trade relations. Over time, the metric system has been accepted in many European countries: Belgium, Netherlands, Spain, Portugal, Italy and a number of American countries: Colombia, Mexico, Venezuela, Brazil, Peru, Argentina, etc. However, not all countries have accepted these units. For example, Congress has twice voted against the "Law on joining the Metric System". Only at the end of December 1975 the US adopted law, but switching to the metric system continues today. European consumer (except English) it is difficult to operate pound, all units which have already become unusual. The English say, a facetious tone, that their country can become an island in all respects, unless they switch to the metric system. But even in countries that have signed the Convention Metric System have kept some national units. For example, calculations are performed on the stock triple ounces (31.1 g); precious stones are expressed in carats (0.2 g); pipe - the inch (25 4 mm); oil - the bars (158, 76 l); floor space - the mat (1.5 m 2). Football gates have width 7.32 m and height - 2.44 m.

These values have been preserved from the British (country football) who provided gate: width - 24 feet (30.5 cm) ; and height - 8 feet. Yet, more and more countries adheres to the metric system. Contributed to the international unification of units of measurement and exhibitions world in which diversity of units were impossible to compare features exhibits. Exhibition in Paris (1867) was the Committee for the measures, weights and currency. The Committee recommended to the International Convention founding an Office of Weights and Measures in Paris as neutral scientific institution for keeping and checking their prototypes international and national copies. The successful implementation of the decisions taken was required formal approval by the States concerned. Standing Committee has made great efforts to convene a diplomatic conference for the development and completion of the Meter Convention. This conference was history measurement units 67 MODERN PHYSICS AND TECHNOLOGY, vol. 7, no. 1-2, 2009 held on March 1, 1875 and brought together representatives from 20 countries. In the last meeting of May 20, 1875, through joint efforts backed by leading personalities, among them scholars known, and given the advantages that this metric adopted on that date in many countries, was signed an act diplomatic particular importance in the Meter Convention, which has become a metric system of units applicable in all signatory countries of the Convention.

The Convention was signed by representatives of 17 countries, except England, the Netherlands and Greece have signed a few years. However, the signatories pledged to found and maintain an International Bureau of Weights and Measures (BIPM) composed of 14 members and a permanent laboratory research in metrology based in Sevres, Paris, whose work is guided by International Committee for Weights and measures (CIPM), over which it has authority General Conference on Weights and measures (GFCM), composed of representatives of all countries adhering to the Meter Convention. General Conference on Weights and Measures meetings shall be convened every six years involving proxies in all signatory countries, each having only one decisive vote. [5,6]. Although the signing of the Meter Convention was accepted concept of system units, in the sense of logical constructions and consistent as it was metric subsequently were created and were applied, starting from this system units, many systems measurement units adapted to the stringent needs of science and technology. The presence of numerous systems units, joined by a large number of Units that were not part of any system units, had in the first half of the last century a negative influence on relations between countries of the world. The call for a "practical system of units likely to be applied in all countries that signed the Meter Convention". Such a system of units based on MKS system was adopted at the 10th Conference GPM (1954) and called on the 11th CGPM (1960), the International System of Units (SI). International System of Units, is a modern version of the metric system, is a practical, coherent, simple and rationally structured, applicable to all areas of science and technology, is used at present legally in over 125 countries.

SI units are used even in countries that are not yet signatories to the Meter Convention, and in countries where legal and other systems used units. Nowadays, it acts alleged, based on international and national programs, to generalize application of IS units in all countries, both at national level and in international relations. Units that are not part of the IS and are not allowed to be used for an unlimited period in parallel with IS units are scrapped or apply restrictions. There is therefore significant scope for units over a few years and become "Using your measuring units for all peoples and all times" as creators wanted a Metric System. An important role in improving the IS and IS units in their spread in the world, they have primarily GFCM CIPM and BIPM and the Consultative Committee for Units (CCU), an organ of the CIPM.

A contribution of great significance in improving and in the spread of IS in the world have also other international organizations active in the field measurement units, among which the first place is the activity and contribution, the International Organization for Standardization ( ISO). In Moldova, IS units and their multiples and multiples used in accordance with Law of metrology adopted by the Moldovan Parliament on 17.11.1995. It includes base units and supplementary units IS units derived IS adopted by GFCM rules for using IS prefixes and training, name and use of decimal multiples and submultiples of IS units, multiples and multiples decimal preferential of IS SI units and derivatives, which are defined as 68 units of physical history and modern technology, vol. 7, no. 1-2, 2009, by units and adopted by the GFCM. And it is described in ISO 1000 and the ISO 31-0, 31-12 ISO, which deals only with the sizes used to describe the physical phenomena. In SI, base units, described by ISO, are seven: length, mass, time, electric current, thermodynamic temperature, amount of material (amount of substance) and light intensity. Each base units (base) is associated with a size represented by a literal symbol, in compliance with the above order: L, M, T, I, θ, N, J