**2. History of information**

Need in time measurement arose about 5000 years ago, around a transition from nomadic to sedentary lifestyle, farming and cattle breeding. In particular, need in observance of optimum time for agricultural work and coordination of collective actions caused invention of different methods and devices for long and short time period measurement that were based either on uniform or periodic natural processes. Diurnal solar motion started to be used for time measurement in Ancient Egypt about 3500 B. C. Obelisks of a certain height ("gnomons") were installed in strategic locations to mark noon with the shortest shadow. Two thousand years later the Egyptians invented sun-dial, "face" of which was divided into 10 parts. By the beginning of the Common Era in Mediterranean industrialized countries more than 30 kinds of sun-dials were used. (Mihal, 1983). In order to measure short time periods, such uniform natural processes were used as flow of liquid or light sand through a narrow hole. Sand and water clocks based on this principle were widespread in the ancient world and sometimes are still used nowadays.

First stellar work for the purpose of time measurement began about 600 years B. C. by means of the astronomical tool "merkhet" (http://www.infoniac.ru). After mechanical spring-actuated and pendulum clocks were invented in the early XIV century A. D. in Europe, precision of time period measurements considerably improved. Pendulum clock constructional design was improved by Galileo, Huygens and Hooke. On the basis of their work in the XVIII century wrist watch was made, it was 5 seconds in error and its manufacture started in the XIX century. (Pipunyrov, 1982).

The XX century was characterized by huge scientific and technical progress in terms of mastering new time measuring methods and devices. First in 1920 by Short, and then in 1955 by Fedchenko the best astronomical pendulum clock constructional designs were developed, they were 2ms/per day and 0.2 ms/per day in error respectively. (Bakulin & Blinov, 1977). Quartz-crystal clock, invented by Morrison in 1927 and based on the piezoelectric effect, opened up new possibilities for improvement of time measurement and time keeping. By the mid-1950s time scale, determined by thoroughly investigated quartz crystal clock, started to serve as an independent time standard, more stable than diurnal rotation of the Earth. As a result, the possibility to detect instability of earth time scale first appeared, as well as the possibility to detect nonuniformity of the Earth's rotation. But quartz crystal clock grave disadvantage was that they could not maintain stability over long time periods because of quartz ageing effect (Great Russian Encyclopedic Dictionary [GRED], 2003).

A complete swing-round in terms of time keeping occurred after atomic and molecular frequency standards were invented. In 1955 the Englishman Essen developed the first atomic frequency (time) standard by means of a cesium beam. From that moment on atomic

A comparative analysis based on the main metrological characteristic of the modern methods of ERP determination and prediction is conducted in the sixth paragraph. The ERP prediction accuracy requirements for the time intervals of the coordinate and ephemeris support of GNSS operation are given within the scope of metrological support issues of coordinate and navigational determinations for GPS and GLONASS GNSS. The basic principles and approaches used by authors for the development of new high-precision ERP

Need in time measurement arose about 5000 years ago, around a transition from nomadic to sedentary lifestyle, farming and cattle breeding. In particular, need in observance of optimum time for agricultural work and coordination of collective actions caused invention of different methods and devices for long and short time period measurement that were based either on uniform or periodic natural processes. Diurnal solar motion started to be used for time measurement in Ancient Egypt about 3500 B. C. Obelisks of a certain height ("gnomons") were installed in strategic locations to mark noon with the shortest shadow. Two thousand years later the Egyptians invented sun-dial, "face" of which was divided into 10 parts. By the beginning of the Common Era in Mediterranean industrialized countries more than 30 kinds of sun-dials were used. (Mihal, 1983). In order to measure short time periods, such uniform natural processes were used as flow of liquid or light sand through a narrow hole. Sand and water clocks based on this principle were widespread in the ancient

First stellar work for the purpose of time measurement began about 600 years B. C. by means of the astronomical tool "merkhet" (http://www.infoniac.ru). After mechanical spring-actuated and pendulum clocks were invented in the early XIV century A. D. in Europe, precision of time period measurements considerably improved. Pendulum clock constructional design was improved by Galileo, Huygens and Hooke. On the basis of their work in the XVIII century wrist watch was made, it was 5 seconds in error and its

The XX century was characterized by huge scientific and technical progress in terms of mastering new time measuring methods and devices. First in 1920 by Short, and then in 1955 by Fedchenko the best astronomical pendulum clock constructional designs were developed, they were 2ms/per day and 0.2 ms/per day in error respectively. (Bakulin & Blinov, 1977). Quartz-crystal clock, invented by Morrison in 1927 and based on the piezoelectric effect, opened up new possibilities for improvement of time measurement and time keeping. By the mid-1950s time scale, determined by thoroughly investigated quartz crystal clock, started to serve as an independent time standard, more stable than diurnal rotation of the Earth. As a result, the possibility to detect instability of earth time scale first appeared, as well as the possibility to detect nonuniformity of the Earth's rotation. But quartz crystal clock grave disadvantage was that they could not maintain stability over long time periods because of

A complete swing-round in terms of time keeping occurred after atomic and molecular frequency standards were invented. In 1955 the Englishman Essen developed the first atomic frequency (time) standard by means of a cesium beam. From that moment on atomic

prediction method are set forth.

**2. History of information** 

world and sometimes are still used nowadays.

manufacture started in the XIX century. (Pipunyrov, 1982).

quartz ageing effect (Great Russian Encyclopedic Dictionary [GRED], 2003).

radiation periods, is considered to be the world time and frequency standard. Atomic time standard is free from both diurnal and secular variations, does not have ageing effect and is characterized by sufficient determinateness, precision and reproducibility. With the use of atomic frequency standards, time standards independent from the Earth's rotation were developed, they are characterized by exceptionally high stability over long time periods. It enabled to fulfil the task of large distance measurement metrological assurance. Precise time measurements are also required to fulfil different tasks of navigation, telecommunications, terrestrial and extraterrestrial navigation, geodesics and geodynamics. They are also used in traffic control systems, information technologies and other spheres. A series of basic researches – aimed at a more precise definition of principal laws of nature related to extension of knowledge concerning Macrocosm, Aerospace, Earth, Microcosm – require such a precise standard that approaches to a limit determined by fundamental physics laws. Thus far the highest level of relative precision of playback of atomic second of the order of <sup>16</sup> 103 was reached by the American National Institute of Standards and Technology (NIST) by means of caesium fountain clock. In the years to come, a new generation of frequency standards that radiate frequencies not in microwave but in optical spectrum is expected. Optical clock is developed especially actively in Japan. For example, Hidetoshi Katori's group of Tokyo University has already reached precision of the order of <sup>15</sup> 10 by means of an experimental model of strontium optical clock, and theoretically they can maintain precision of playback of time and frequency units at <sup>17</sup> <sup>18</sup> 1010 (Hall, 2006).
